For a great price, you can get them at CVS. Last week, they had a buy-one-get-one-free sale on CVS brand joint supplements, so I was able to get two bottles for $50, which is nearly a year's supply for one dog.
CVS Brand
Glucosamine & Chondroitin Triple Strength
180 tablets for $49.99
Contains (per 2 tablets):
Vit C 60 mg (100% daily value)
Magnesium Sulfate 2 mg (100% daily value)
Glucosamine HCL 1500 mg
Chondroitin Sulfate 1200 mg
**Contains NO yeast, wheat, milk products, lactose, sugar, soy, preservatives, or artificial flavoring
I ran it by another member on this forum who is very knowledgeable about this kind of stuff and she approved it. I give one pill per day for supplementation/prevention.
I also use Nupro Joint Formula -- GREAT for all around health support, with added glucosamine, chondroitin, and MSM. You can get a good deal at online pet supply places (couple months' supply for like $35-40). It's a yummy liver flavored powder you put on the food that makes a gravy when mixed with water.
Ruger and Sasha get the Nupro with one meal, then one joint pill with the other meal, so they don't get tired of the same liver flavor all the time. I also give the pills occasionally to Nico (who has excellent hips on x-ray) because he can't have the Nupro, as he's allergic to the beef liver.