Entropion is the rolling inward of the eyelids. It is more common in dogs than cats. Cats often develop it secondary to other problems including pain, infections, scars and nerve damage. The signs are squinting, tears, a mucous discharge, rubbing the eyes and other signs of pain.
Mild cases that do not produce much pain (tearing, squinting) can often be treated medically using a eye lubricant (artificial tears, eye ointment). Definitive treatment requires surgery.
The cost of surgery varies depending on where you are and who does the surgery. Did you ask your vet this question? He should have an idea of what the costs are at the places suggested.
Let me know if you have follow up questions.
Your vet can't quote a price, but vets can often give an idea of cost range.
The vet who will do the surgery will want to see the cat before giving a reasonably accurate estimate. The cost will depend in the amount of correction required. You can call and ask for a range.
I'm on the opposite coast and have very little idea of west coast costs.