Those prices seem a bit high, if they are US dollars. To rebuild just the roll drive shafts and bevel gears for a 4 row will run over 2 grand CAN., not to mention any other parts. low acre units for $3000 or less are out there, usually a privately sold one can be had for a decent price. Sometimes a 'non AC' dealer will have just a header for sale, a little dickering will remove the 'orphan' from his yard. The double bevel roll drive gear should have less than 1_8 inch lateral play; if there are some shims left behind the bearing housing, remove some to get this clearance and it should be good for many acres. Splined couplers and shafts should be checked for looseness, they cannot be adjusted and are expensive to replace.