I'll tell you the truth: I've been a boater since I was tiny. I got my first boat when I was 12 and I've owned probably 10 since. I also worked at a marina for a few summers and one of my side gigs is buying up junk outboards and putting parts from three together to make one, and things of that sort.
Nearly any outboard before about 1998 is almost bulletproof. I have an 88 Merc 70 that I wish I had bought an hour meter for it. Every summer since 1988 it has been used HARD in salt and fresh from late May to early September. When I say hard, I mean a typical day for it goes like this: morning fishing with a lot of trolling for three hours at a time. Day trip on the lake usually with an hour or so of skiing, tubing, kneeboarding, and hooning. Evening fishing trip with another couple hours of trolling. Finally this last summer I had to replace the fuel pump and the stator. I currently have two Evinrude 30s from the early 80s that I'm putting together to make one, but they both run despite looking like they have been through a nuclear explosion.
Force motors of yore are Chrysler designs that should be avoided at all costs. About the time Force was bought by Merc/Mariner, Mercury started outsourcing and cheapening things. These days if I were buying new, I would buy a Yamaha or Suzuki. In fact, I have a Yamaha 50 on a pontoon now. I think it has four years on it now and I love it.
I wouldn't hesitate to buy a used outboard. Parts are everywhere and cheap. Replacement parts are interchangeable across decades and multiple models.
I really get so frustrated with folks who talk about "hole in the water you throw money into" and "bring out another thousand." I've had some boats for 15 years and didn't put a single penny into them. The two 30 horse Evinrudes I have I paid $25 for the pair; $12.50 each. And they run. And I wouldn't mind putting them on the lake tomorrow. Once I fix them up, I'll probably buy a $500 aluminum boat and I could probably run them for another 15 years.
Recipe: Find a late 70s - early 90s OMC in the horsepower you want. If it runs, you know that anything it needs will likely be small and cheap. Things to check: Where the pull cord and/or starter engage the teeth on the flywheel, look for wear in the teeth. That is a vague indicator of how much its been used. Pull the drain plug out of the lower unit. If its cloudy/milky, has water come out first, or has flakes of metal, you might want to look for another option first, but water is not necessarily bad. It rarely means there is damage (unless you see flakes), but it may indicate that the shaft seal needs to be replaced. The big consequence of having water in the lower unit is freezing/cracking. Start it on water muffs and listen. Then watch the pee stream. Make sure its steady and strong. When hot, it should be almost too hot to keep your hand in. If the pee starts and stops, don't panic, it just means it might be a model with a thermostat. (or it has a prostate problem).
For comparison sake, I just sold a 92 Merc 25 EL (electric start, remote control) with the controls for $1000. They bring pretty money. But buying an older outboard is kinda like buying a 1978 Mercedes diesel. It will cost pennies, but probably run forever.