I used to restore old tractors, including a 1964 MF135 diesel. A labor of love, but time-consuming and, at times, expensive. Your go-to tractor should have less than 1000 hours showing on the gauge and should have a front end loader (FEL) and a 40 hp (engine) as a minimum requirement. Plan on spending $10-12K.
Good luck
Jon1, I got curious about the thread title and read through it. Here you have two pages of replies and all saying essentially the same thing. That may be the first time that has ever happened on this forum! At any rate, it's rare. And this from a whole bunch of older guys who have owned lots and lots of used tractors. And they are guys who generally like older tractors. That includes me, and I find myself agreeing with everything I've heard here.
We did exactly the same thing you are thinking of, and bought a a 30 year old John Deere model 530 to build our house. It had almost 9000 hours, ran fine, and we paid about what you are looking to spend. That was many years ago and it still works the same as it did then. We still have it. It's a family member now.
I think you will find a good used ag tractor for between $4000 and $10,000. For that it should have good everything. Probably a decent loader, definitely good engine, tranny, and hydraulics. It will have a dandy 3pt hitch and I'd be surprised if it didn't come with a basic implement or two. There are a ton of tractors out there just like that. We all follow the market and you are getting good advice so far. So wait for it. Your's will be coming along. Look at used advertisements in feed stores and in smaller farming towns where everyone knows everyone. Tell your story. In the meanwhile, hopefully you can find a local guy who is will help you look. You'll be time and money ahead.
BTW, that guy who told you anything that sounds like his son, "forced the hydraulics into gear"....well, he doesn't sound to me to be the right person to turn to for tractor advice. I've only been a mechanic for 50 plus years and never heard that particular expression. But I think I do know what he is referring to on Masseys. And if I'm right - or anywhere close to right - then you best stay away from both him and that tractor.
You are in a reasonable price range where your money will buy you an excellent older tractor in good working shape. I do hope you get the loader, but it is the tractor that you really need. Oh, and do get a tractor with a wide front. 4wd is not necessary in an old ag tractor, but a wide front is. You do not want to be using a loader with a tractor having a single narrow "row crop" type front wheel set up. We've all done that, and the pity is that there are some darn good row crop tractors out there for even less money. But they are just too unstable.
Good Luck,
rScotty