I have wondered the same thing. My 8 yr old GSD has become more noticably reticent to get up and go for stuff. She groans audibly when she lies down these days. So, I went "in search of" something to help without breaking the bank.
She is a picky eater and is already on anti-seizure medication and thyroid meds... so I can't afford to spend ridiculous sums on joint meds, or specialty foods, too.
I went to PetSmart and checked out their medicinal aisle. Ended up getting a tablet with 400mg Glucosamine and Chondroitin (the same stuff dr's recommend for humans with arthritis and joint pain) for her. A 4 month supply was about $27. I just add one tablet to her daily food, just like I do with her heartworm medication tablet (that's just once a month though, lol). She just eats it along with the rest of her dry kibble. Her actual prescribed medication, I have to give her twice a day, and that requires the pricey pill pockets to get her to take them.
I haven't had her taking them long enough to really tell if they work (the packages all say 4-6 weeks for noticeable results), but unless I am just wishful thinking(seeing)... she gets up more readily now than she did just 2 weeks ago (right before I started her on this tablet). She seems a bit more spry already.
And FWIW, do your research on Rimadyl before going that route. It is a controversial drug. There is some scary information about it out there. Our dog was given Rimadyl for a high fever and other issues about 2 years ago. I cannot for certain say that the rimadyl is the cause, but within 24 hours of taking it, she had seizures, dizziness, balance issues, loss of ability to stand, etc. These dragged on for a week, and we thought she was going to die several times. We took her to a 2nd vet for a 2nd opinion and had her admitted for hospital care. She made it. It may be that the condition that prompted her original vet to prescribe the rimadyl was responsible, or it may have been connected/side effects/contributed to by the rimadyl. We'll never know. But Pfizer even keeps a record of "adverse reaction" incidents reported. And there is a support group for animals who have had severe adverse reactions (which in some cases are fatal). So do your own research before blindly using it on your dog.
ETA: here is a link to what I buy:
http://www.petsmart.com/product/index.jsp?productId=36204...