CPK

You need to forget about the motor, and disregard the electronics ( they are old and have little resale value).

You need to determine what is a fair price for the hull (assuming it is in great shape), and most importantly - what the hull is worth to you.

Base your offer on that. The motor is a crap shoot at best and you should not be spending good money on that, even though that is what the broker has convinced the owner that he will find someone willing to do that. If the motor was a reasonably easy fix - the owner would have done that.

Try to get an idea of:
How long the broker has been trying to sell the boat?
It is the end of the season - what happens if boat is not sold? Does boat go back to owners property or does owner pay to store it for winter with broker?

You hold all the cards. Good luck.