Every vet will tell you that Hill's Science Diet is an excellent brand that they don't give to their own pets because it's too expensive.

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.

That sounds like a really shitty vet. I would stop going to one who is peddling products to me that I can’t find anywhere else.

There are quite a few online shops selling Luxottica, it is that they use their brick-and-mortar presence as a front for their online business.