Thats reasonable! Does that include the computer and wiring? For $500 I'd talk him into it, whats that "crap" worth to them anyways. See if he'll do it for less even!
But seriously, before getting it, I'd want to hear it running. Let it warm up and check it over well, cold and warm pressures, sounds from inside.....compression.....you know, the usual
And if you don't go for it, lmk!