In reality, nobody is likely to pay these prices. So.... where do people get the parts from?
AIUI, if you pick up an old door from some scrapped aircraft, and get an engineer to sign it off as sound, you can install it. The US must be full of aircraft breakers yards.
I'd get onto google.
In this business, "connections" are everything. This comment won't apply to a Cessna door but knowing the real manufacturer of some common part (e.g. a door strut) is very useful info.