TOPIC: whats a fair offer?

found a Merc 115 w/ controls and trim on CL
bad cylinder they have removed some of the piese to inspect.
seller pruchased different motor for boat and trying to sell.
they are 2hrs from me and asked me for an offer, i told them i would look up repair parts and w/o seeing it was hard to determine...

I've been hunting for a 90 tower, but this is the dirst 115 i ran across seperated from a boat.?

so whats a fair offer w/o ticking seller off?