I devote a lot of my time to breed rescue in a poor region of the U.S. where many people who want to adopt have little money. I know many solo-rescuers who take on dogs they can't afford because if they don't, the dogs will die...so they do the best they can, knowing it's more than anybody else is doing for the poor dog. I'm not going to judge them for taking on dogs they can't fully vet if the choice for the dog is their help or no help. I'm also not going to judge people who walk away from helping because they don't want to go into deep debt for a dog.
Our world is full of suboptimal choices. Here's the dilemma -- and it really is one -- for a dog in a bad situation:
Get adopted by someone who will love the dog and give it daily care to the best of their ability...and just hope for the best, even though the person can't really afford major vet care. For a dog living on a chain or in an abusive or neglectful environment, this is a massive improvement in life--it means being loved, and for a dog that otherwise isn't, that's a big deal.
Or hold out for a better home, because each of them deserves to get excellent vet care, with a long healthy life. For rescuers, that means saving fewer dogs overall and accepting that there will be deserving dogs who don't get homes at all. And for the dog on the chain or in an abusive or neglectful environment, it means being left in place because that perfect home isn't available right now. Making peace with that is hard, but it's sometimes necessary.
OP, you're only thinking about one dog, but it's the same sort of dilemma every rescuer wrestles with in high-kill regions of the country where there are more great dogs than great homes. There isn't a right answer to it -- rescuers argue about it, cry about it, and rescues literally blow up over it. I can think of one city with multiple GSRs *because of* philosophical disagreements over this kind of question. We all have to make a choice we can personally live with.
I'd ask you to think on a few questions:
(1) How bad is this dog's current living situation, and does he have other options? If you're his only option, could you perhaps resolve to be his foster and eventually find a home that can afford him -- in other words, might you just be the bridge out of there? If you can't adopt or foster him, can you network him to good rescues to help get him out of there?
(2) Will your financial picture be improving? If so, realistically, how long will it take for your income to improve? Are there secondary income sources you can tap to create an emergency fund for the dog? One of my friends who's a solo rescuer works extra shifts to pay for her vet bills for the dogs she takes on. She can't afford what she does on her regular salary, so she uses the extra shifts to do it (sometimes working 12 hour days, or 7 days a week). Another one I know drives Uber on weekends to pay for dog stuff. Not everyone wants to work extra jobs to pay for dogs though -- and it's reasonable to say that's just too much to take on. That's a very personal choice.
(3) Can you put major vet expenses on credit? For example, can you qualify for Care Credit to help with big vet bills? Or do you have a credit card with a high enough unused limit that you could keep on reserve for vet bills? You'll still have to pay it down, but at least you'd get a year or more to do that. Not everyone has good credit though, so this too can be a barrier.
(4) Does your region have a low-cost vet option, even if it means driving a bit to get there? You might have to call your shelter or a few rescues to ask about this, if it's not known to you. Thrive Clinics inside PetCo and VetIQ inside Walmart are both driving down vet care costs where they are opening. My city also has a "no frills" high-volume vet clinic in a blighted part of the city that people drive to in order to get low-cost care -- it's a run down building with folding chairs in the lobby, but xrays would be no more than $100 at this place, and they're all about finding cheap ways to fix dogs in need. In more rural areas, farm vets who have clinics set up in their own barns sometimes offer similar low-cost, no-frills care.
Here's my take on your situation:
I wish everyone who adopts a GSD could afford excellent vet care. I also don't want to see anyone go into debt for their dog. Life is messy though, and sometimes we all just have to do the best we can, especially if a dog is in a bad situation.
Having taken on lots of rescued dogs with HD, those hips wouldn't scare me. I've known countless GSDs that have lead happy, active lives with HD--never needing surgery. The key is they were managed well by diligent owners... but that need not cost a fortune. On of my own elderly dogs right now is old as dirt (over 12...we don't really know), blind, with crappy hips, and he walks several miles a day and is out hiking with my DH now. We limit him to a few miles, but he loves doing it. My personal dog is 8 with bad hips, and we've been hiking 3-5 miles a day during our summer break in the Rocky Mountains, and the dog is never happier than we're on a trail. Walking as much as they enjoy is good for them, maintaining muscle tone and loosening up arthritic joints.
You don't have to be able to give them $5,000 bilateral hip replacements to be worthy of owning them. Sometimes, a $500 FHO will give the dog a good, pain-free life. And many dogs with HD do well with medical treatment without ever needing any surgery at all. My friend's adopted GSD has the worst hips her vet had ever seen, and the dog is still active and going strong at 12 years old (after years of being kept lean, active, and getting regular Adequan injections).
If you're going to take on the dog, the low-cost, minimally invasive way of managing it is as follows:
-Find an inexpensive vet willing to start the dog on "generic" Adequan ASAP -- the off-brand version is called Ichon and available from Valleyvet.com for about half what Adequan costs. Ask the vet show you how to do the injections yourself (2 per week for 4 weeks = 8 injections, then maintain once a month, in a young dog). This will help stop joint degeneration and preserve cartilage, lubricate the joint (= heal), and in about half of dogs, it's anti-inflammatory (= pain relief). Many vets don't know this generic option exists, and it's technically an off-label use of it, but it's the same active ingredient as the expensive branded stuff -- vets that do a lot of rescue work or serve a low-income population are more likely to know about it. To estimate cost: as a very rough rule of thumb, a 75# dog gets approximately 6 injections out of 10 ml (which costs around $50).
-Start the dog on good supplements (lots of threads on that here)--you don't have to spend a fortune on branded supplements. Some of the recommendations (like bone broth from chicken necks and backs), you can make cheaply at home.
-Work with your vet on a good exercise program to strengthen the rear end without impact (e.g., walking on hills, swimming, etc.). This need not cost anything more than your time, especially if you can find a friend with a pool who doesn't mind the dog in it.
-Use pain meds as needed until the Ichon kicks in. Generic carprofen is less than $30 for a big bottle of 60 from an online pharmacy like Valleyvet, and you'd need no more than 2/day (maybe just 1) in the proper dose. Other NSAIDs cost far more, but if the dog can handle carprofen, pain meds can be very inexpensive. Your goal is for the dog not to need it, once the other stuff outlined above is working. We use this stuff at the lowest effective dose, which is often considerably less than the official range (I've seen some dogs get relief at HALF a normal dose). You know its effective when the limp stops. We run bloodwork on dogs on it to verify that they're metabolizing it, and this is about $100, but that's a matter of your risk tolerance -- some low-cost vets don't run the bloodwork because the odds of a reaction are so low (though potentially deadly).
-Budget for an FHO performed by a general-practice vet who happens to have a special interest in orthopedics and is good at them, if you can't afford a specialist. That's the least expensive surgical intervention, but it may not be needed for years with a good management plan described above. Find out who that vet is locally (again, the rescues will know), and get an estimate. Our rescue's vet is that vet in our region -- she's done a huge number of FHOs on dogs who don't have other options, and they do just fine. They won't ever be athletes (definitely no agility!), but the pain stops and they live with good quality of life.