Anywhere between $3000.00 and $8,000.00 depending on how equipped and condition. High hour, 2wd, no loader maybe less. Hard to say without more details.
Those are 2 features that will make that machine an easier sell, at a good price.
The 1900 appears to have an original 1982 price of $8350 without loader (?). A good condition tractor with NO issues and reasonable hours should sell for about its original sales price.
Assuming good condition with say <2000 hours, I think I would try asking $10k and see what happens.
I sold my Ford 1900 4wd with 1000hrs on it several years ago for $6000. I listed it for $6500 and they guy offered 6 so it was gone. No loader on mine and he was actually asking about where he could buy one for it. I told him look to equipment dealers for anything like that.
My guess is yours is worth about the same. Mine had no rust anywhere and the paint was perfect and tin had no dents. Mechanically mine was in good condition not perfect condition. (radiator was the weak point and had been repaired the year before for leaks)