Your in Big Ag land so finding one shouldn't be too bad especially in a month or so when everyone is cleaning out their barns and deciding its time to sell that old tractor in the corner.
Ones that I would look at would be Oliver Super 55 or 550, AC D-15 thru 17, MF 135 or 235, International 404 or 504, Ford 860 and 960. As Dan said as well as other posters the parts for SOS transmissions are getting hard to find. Clutches, Brakes, Seals and bearings are all readily available for all makes through places like Steiner tractor parts, ebay and other online parts stores.
These are all in about the 40 hp range and should run a small triple or definitely a double bottom plow. If you planning on tilling about 2-3 acres it should suffice. If you are looking at going larger you will want to probably step up and go with a tractor with rear remotes running larger implements.
I paid $2500 for my oliver Super 55 and it has been a great tractor. Roughly 35 hp which sounds light on the HP side but it does everything I need it to do. I run a pto manure spreader, 8' grain drill, JD 290 planter, 8' lime/seed drop spreader, 6' bush hog, 6 1/2' double gang disc, and 2-14 double bottom plow and it doesn't struggle in the least with any of them. Bought all this stuff off Craigslist in the last 5 years or so and have less than 4k invested including the tractor.
I put in about 3 acres of food plots and personally for me I don't need anything larger.
Search craigslist in your area when you find something that might work look it up on tractordata.com and go to youtube and search with the model and make. There are tens of thousands of videos of people working their tractors on that site.