I bought a
B2150 last year for $4500, an HST with no functional problems and a midmount mower. Four or five years ago I bought a
B2150 stick which lacked a mower for $4800 I think it was. All good. No problems. Potentially the slipping out of gear on the 1750 can be repaired externally without tearing down the tractor but I do not know them well enough to say that. I had exactly that issue with a MF2660 (coming out of 2nd gear very frequently) and the dealer repaired that without tear down. Some small piece inside the trans was broken but could be replaced.
I'd have a talk with a very experience Kubota mechanic and get some idea of how big a problem that is.
How many hours? If the trans can be fixed for a few hundred $ and the tractor is not high hours the price is probably reasonable since it has a loader. Everything else seem to work OK ?