My 4 year old cat has struvite crystals?

my 4 year old cat has struvite crystals...she had a UTI in August, at which point there were no crystals, then about 3 week ago i rechecked the urine and sure enough there are struvite. she was always fed grain free dry foods (innova evo, solid gold indigo moon, etc) so i thought i would be ok, but apparently not. now both my cats are eating strictly wet food but i am wondering what brands people have had luck with in the past because this is killing me financially. i refuse to use the hill's foods (i'm a vet tech, i know they are crap) so i'm trying this route of doing only wet food and right now i'm using wellness grain free chicken or turkey. its costing me about $30 every 8-10 days and i dont know how long i can keep up with this! is it ok to use a lower quality food, as long as its wet? or does it really need to be grain free, etc.?