New Powerhead?

[qdive1]

Hey Guy's I'm a newbie to this site and just bought my first boat. A 1986 V20 Step/Lift in very good condition with a 1986 Evinrude 150 all original as it came from the factory. The only problem so far is a big one, I did not do a comp. test on the motor when I bought it as it ran great on the guy's driveway until I took it out for the first time 3 weeks ago. It was a bit rough to start up at the doc but It got up on plane quick with what seemed like plenty of power to me I thought but at WOT would only do 4100 rpm @ about 29 mph (GPS) and after 10 min. or so lost power down to 3000rpm at WOT and totally stalled and would not start. I was able to get it back running by choking it and I returned quickly back to the dock when it stalled again when I idle it to try to load it on my trailer. Bottom line, #5 cyl has only 20 lbs of compression and metal fragments on spark plug, all other 5 at 65-70 lbs comp. My question, I can’t afford a new motor at this point and my thoughts are if I buy anything used for $ 3500 or so which is what I can really afford at the moment It would be a roll of the dice that I get a good motor. I was thinking of doing the powerhead from a local guy here in Tampa, he asking $2380 with a 1 yr. warranty and he does all the work I just take him the boat. Is this a good price?, I would think it would be like an almost a new motor and I would know all major components had been changed, ie: new pistons, rings, bearings ..any Input would be appreciated as it's a big chunk of change any way I go but I really like the boat and think it's worth it.

Thanks !!