I had a male kitty (RB) with UTIs all the time....and we finally ended up putting water in his canned cat food - making him lick the liquid off to get to the meat portion. I also bought only canned food with a very low ash content. It seemed to help. I think the Vet could recommend a good food for your kitty's problem. Poor kitty..... poor wallet. Been there, done that. Gotta do it, I know.

Paws and toes crossed that Fister gets well soon!