At least in the US, you can still find "vintage" tractors like the Ford 8N or an old Allis Chalmers or Farm-All, which were sized for much smaller fields. They

At least in the US, you can still find "vintage" tractors like the Ford 8N or an old Allis Chalmers or Farm-All, which were sized for much smaller fields. They're simple enough machines and you can still find parts for them; if you want to add machining to your skillset, you can also find the manuals that tell you how to machine new parts yourself.