I had every intention on rebuilding the "heirloom" 102 I used to mow lawns with when I was a teen. Then, I picked up an old 129 as a possible project, or for spares for my 102, not really knowing what a 129 was at the time. The 129 was pretty much a wreck when I got it, but with a good deal of patience, and some luck finding a usable engine block, I got her running and have been tinkering with it ever since, and plan to tinker with it some more soon (adding a hydraulic lift). I run the crap out of it blowing snow, and cutting 2 1/2 to 3 acres of grass every week.
Then I found out my neighbor had a 125 when they stopped by while I was building up the motor for my 129. They told me they were having trouble getting it running, so we towed it over my place and after a couple of hours of work redoing the carburetor and swapping a few ignition parts to troubleshoot it, I had it running better than I ever remember the old 102 running. I probably could have talked them out of the 125 for half of what I ended up putting in the 129, but by then I was already in pretty deep, but still only maybe a third of what a Huskee/Craftsman/Murray would cost.
Well, I found another 102 on Craigslist last summer, thinking I might have a parts tractor to help fix my 102 heirloom, but this parts tractor looks to be a better restoration candidate than mine, so I'm restoring it instead. Everything's pretty much done but the paint and reassembly.
And so it goes, you'll always find a better deal out there somewhere, usually right after you decide to pony up for something else. Its a constant learning curve that's part of what makes it fun!