E.T.
Hmmm... our vet diagnosed our elderly cat with a similar problem (UTIs and reduced kidney function) and told us to get Hills prescription c/d at the pet store. It's $1.59 a can at Petsmart, slightly less if you order online, but I don't think you'll save much versus getting from the vet.
The vet also told us that some of the higher quality wet foods might also work. The brands were Natural Balance, Simply Nourish and Soulistic. You can save a bit with these brands, especially if you buy when they're on sale. We have had good luck with Natural Balance Duck & Green Pea canned food for our cat.