Depends on where it is as well as condition - the $4000 one was completely restored 1949 tractor and had discs and other accessories that are rare. I have seen them go higher - that may have been one of the relative "bargains" of the Zacheis AC auction.
If you are in Louisiana looking at a complete but not running UCHC straight out of the canefield its more like $800-1000 if its in decent shape. If its too rough, it may be closer to scrap value - say $400-500. If its in good shape and running good, asking would be closer to $2000-2500, but selling price probably no more than $1500-2000 down here. Same tractor up north - maybe add $1000 which is probably what it would cost to haul it up there.
There are some variations that might make it more such as "correct" GM diesel engine but I"ve only ever seen one of those and it was in really bad shape beat to Heck with lots of welding on back and wrong radiator and hood.
When I say "correct" diesel engine I note that all "original" engines prior to end of line s/n 6217 (1953) were Kerosene/Distillate or maybe a few gas burners. But Thomson continued "production" by initially buying chassis units from AC and later by buying and refurbishing U and UC chassis and putting their HC parts on them.
Some of the later Thomson UCHC (UCD) had GM 2-cyl diesel engines. Some of the "refurbished" ones had G226 (D17) motors though most retained the UMA motor.
The "refurbished" tractors have a 5 digit s/n instead of the AC 4 digit s/n. The 5 digits supposedly are the year (63) followed by the Thomson number. I have seen 4 of these - all starting 63 and ranging from 120 to 293.
Correct wheels would most likely be solid "Thomson" centers with 13-38 (14.9-38) R2 tires though I have seen spoked wheels - some with 36 inch tires same as used on the cane carts - but I"m guessing these were a convenience. I am told the French and Hecht spoked wheels from a John Deere are same as those used on Cane Carts.
But as said - its worth what you are willing to pay. If you post more info maybe a picture, it might help.