I wouldn't spend money you don't have on a shotgun-approach to buying expensive supplements...or grooming. Here's my advice to helping this dog on a shoe-string budget:
First, ask your vet to change your next refill of the Rimadyl to generic "carprofen" (same stuff, but in a pill not a flavor chew...Rimadyl is the pricey name-brand version). Then you can fill it at WM Pharmacy, or online. Walmart does
carry carprofen for dogs, as do Sam's and Costco. They sometimes call it "vetprofen" (call the pharmacist and ask before you do the refill, so that the vet can write it the way they want it). With my vet's RX, I can buy a whole bottle of the 60 pills of generic at Valleyvet.com for around $30....two months worth!
Second, price check the Tramadol before your next refill. It should cost no more than about $10. It's a human generic med that you can fill with your vet's RX at any human pharmacy -- prices vary, so use this tool (print out the coupon on the site, and take it to the pharmacy to get the pricing they promise):
2. Supplements -- a lot of high-end supplements are very expensive. Don't forgo meds to by them, and don't spend money you don't have trying to guess. HOWEVER, WM does carry a product in the pet aisle called VetIQ Maximum Strength Hip & Joint -- it's a pouch of chews that sells for about $12 in the stores. It has fish oil, MSM, hyaluronic acid and a few other things. I was expecting it to be low quality and ineffective at that price -- but it's actually surprisingly effective. My dad is on a fixed income and buys it for his old dog, and it's made a significant difference for her. If you can manage $12 extra dollars, that's the one supplement that would be worth it -- I say that knowing every dollar is very precious, and there are none to waste!
3. Shampoo -- I agree with TheCowboysGirl about a medicated shampoo. The one she recommended has 4% chlorhexadine -- very important ingredient to rid the coat and skin of bacteria that can cause itching. If the brand she recommended is outside your budget, there are other brands that are a little cheaper on Amazon, with free shipping:
(Keep these products away from the head--only from the shoulders down so that they don't come near the eyes! They can cause blindness.)
4. The loss of hair around the eyes is sometimes a common thing that happens with mange -- demodex mites infect the dog. Usually that happens when the immune system is running low. They can lose nearly all their fur eventually, and it's very uncomfortable. It's not terribly expensive to treat though at the vet. A skin scrape at the vet is usually needed to diagnose it.
HOWEVER...thinking outside the box about the cheapest way to help...a single NEXGARD pill might be another option. It's a monthly antiflea med...that also happens to work really well on getting rid of Demodex mites. If it's not demodex, he'll just end up with excellent flea protection for the month...and if it is, it will help knock it out. It runs about $30/pill at the vet (or with your vets RX, about $60 per 3-pack online) --