Well, does the seller have any documentation on the build? A 'rebuilt' engine is defined differently by folks..... would depend on how thorough a rebuild it was.... was it bored, new pistons, balanced, heads done....or just a set of rings and bearings?? Value is hard to say. Depends on how bad the seller wants to sell and the buyer wants to buy.... If it's a quality rebuild, maybe somewhere between $500-$1,000???? At least that's about all it would bring around here. Maybe if you can at least hear it run, then more....