Crystals in cat urine, need recommendations

Looking for some recommendations to change my cat’s diet. He has a lot of crystals in his urine and the vet recommended royal canin urinary diet.

The wet and dry food options from that brand are super expensive, I’m wondering if anyone has other recs that aren’t as expensive?

Will he need a wet food-only diet? I add water to his wet food atm and feed him blue buffalo wilderness along with fancy feast wet food.

He generally drinks a lot of water so I’m confused why he has an issue with crystals.