"What is your alternative - a
"What is your alternative - a new engine? or another used engine?
Start with the "no compression" - you may be able to get away with fixing just the one cylinder. That would keep the cost of parts down especially if you can do the work yourself.
If not you can probably count on spending anywhere between 1500-2500 bucks to have it rebuilt.
The "no spark" could be anything from a 30 dollar coil to a couple hundred dollar switch box etc.
At worst, for under 3k you could have a "like new" powerhead (or fairly close).
A NEW 150 will run you 14-18K and buying a used motor could leave you in the same spot you are now a couple months down the road.
If it was my motor and I had been using it, would I fix it? Absolutely, a mid 90's 150 Merc is/was a decent motor..."