My 1983 Baja was a total investment of $3500 and change. (lots of work because it was pretty rotten and needed a new motor). Over the few years I ran it, it cost me zero in repairs and only oil changes for maintenance.
My 1958 Sea King runabout is still on the lake. The original 1959 10-horse Evinrude is still in use (not on that boat, but on another 14' boat. The only reason I replaced it was that it was slow, so I put a 1993 Merc 25 on it... and it is still in use today. The only repairs that were needed for the old 1959 10hp was a driveshaft pinion gear because I completely forgot to put lower unit oil in it one season. $5 at the junkyard and 2 hours of fiddling fixed it.
My current Ebbtide with the 3.0L had a gunked up carb when I bought it, but $1 worth of brake cleaner and an hour solved that issue.
All of my boats have been just bloddy bulletproof. Current and past inventory, just for a reference of things I would recommend and not recommend:
1958 Sea King. 1959 10hp 'rude (amazing), 1976 Johnson 20hp, then a 1993 Merc 25. All recommended.
1968 Glassmaster. First motor was a 1968 Merc 65 that ran for 20 years of my above-listed abuse before it just started losing power/compression. Second was the 1988 M70 that I detailed before and it's still on the boat.
Grumman pontoon from the 80s. The motor that came with it was an early 90s Johnson 48SPL. Nice, but dad didn't want any more 2-strokes (biologist/environmentalist) and he was getting too old to not have power trim, so he got a Yamaha 50. I forget what year, but it was the last year of the carburetors and not EFI. All recommended.
1960s Starcraft. Aside from the rough-ish ride, bulletproof boat. It had a 69 Johnson 70, and it got replaced with a mid-90s Johnson 70. All recommended.
1983 Baja 19 Sunsport I/O. The hull was a full 1-1/4" thick solid glass. No wood in the hull to rot. It was an amazing combination of fast hull with enough deadrise in the front to be as smooth as a cadillac. WOT and 60mph was nothing in a 1' chop. Mercruiser outdrive was great.
199? Ebbtide. Ebbtides are in the middle-range of quality. Mine is great, but with the 3.0L it is much slower than I wanted. I don't think I'll put the money into a re-power, so I'm looking for another boat.
There are so many more, most of which had similar powerplants that I loved. I will echo that you should go as analog as you can. I don't want EFI, electronic controls, and all the junk that goes with it. Just give me a carb, some cables, and a key. This is why I will almost always buy used. I would love a hydrostream, but they frequently rot the cores in the hull. There is a catamaran (forget the brand) that is super fast (like 100+ mph) with a 275 horse outboard, but the layout of cats kinda sucks for my purposes. I would settle for a fish-n-ski type which is basically a bass boat hull with a wraparound console.