100#-150# all within 10%
Your gonna need to pull the head and inspect for whats causing it. Could be a melted piston or a hole - either way probably would need a rebuild. Anything is fixable, just a matter of whether or not you are willing to put the time, money into it. I had the same issue last year on a 89, 90hp where the bottom cyl had no compression - turned out to be a melted piston. I just wanted to get out on the water cause it was middle of summer so I sold it, and picked up an 88, 85hp that runs great.
Believe it or not you can get pretty good $$$ out of them parting them out if your patient. Even with a blown powerhead you can probably get close to 4 digits. Again, that is if your patient, price and sell at the right time, etc. The electronic ignition components and lower unit will be the big $$$ makers.
As far as selling it as a complete blown motor you won't get much in all likelihood. As for rebuilding and selling that is a lot of work and energy that you probably won't see reciprocated in dollars when you sell. If it was me it would be parted out.