hi,

well you might consider buying a used 500 or 380 (usa spec) motor.
another problem with all the aluminum block motors(m116,m117) is that the head bolt threads in the block pull out. another $$$ repair. Most shops today will install a good used motor. doing a rebuild will end up costing upwards of 5k-6k, and they have to warranty the new motor. I don't care how good you think you are, but a factory motor with some miles on it might be better than a tight/loose re-build by the local machine shop.
a used motor(engine. sorry p.e.h.) will cost less that half. just make sure it's a good one and you will keep your cost down.