If, and be warned it might be a fairly big IF. The missing door was a standard size you might be able to find a second-hand door & frame at one of the bigger second hand safe dealers. Obviously you will not need the frame but it should be possible to re-hang the door onto your frame with minimal modification.
It may take a lot of legwork - and you may still be looking at 10K or so that the end of the day.
As a point of interest when did the building cease being used as a bank ? Have you asked the bank what happened to the door ? it may still be sitting somewhere in storage, stranger things have happened !