Headgasket replacement cost

Mechanics will quote based on what you ask for, depend on how efficient they are, and if they want the work.
Challenge in the "fishing estimates" is to understand what's included. Detail, detail, detail. If it's a strip down, machining, checking / new consumables and all service items then sounds good. If it's literally removing the head and stock head gasket replacement, then its way over priced and the mechanics fishing for someone who doesn't know or he doesn't know.
Evaluate your costs of swapping in another engine, either the same n/a or another engine 1mz or 3sgte.
What state are you in?