The "prescription" version is even worse. You need a "prescription" from your vet to buy it for authorized retailers, but it doesn't actually have any drugs in it that are regulated in a way requiring a prescription. They've been sued over this (but I think they won).

My vet told me to put my cat on it after he had stress-related urinary problems. The problems went away, but the food is stupid-expensive, I'm a little peeved at how the system is taking advantage of me, but I don't know what to switch to other than starting to give my cat tryptophan.

Take your pet to a different veterinarian for a second opinion. There has to be at least one that doesn't shill for corporate product and can give you grounded, practical advice.