Depends on condition and completeness.
Most valuable is the sidemount Electrall. If properly advertised and the owner is not in a hurry, it should bring over $5000 and maybe alot more to a motivated buyer.
Next would be a Fast Hitch Electrall. They may have a rarity approaching the sidemount. However, the unit is not as desireable as the location limits other tractor applications at the rear.
Trailer Electralls can be found fairly easily. Good units can be had for between $1500 and $2000.
IH pickup truck Electralls have to be extremely rare. I haven"t seen a parts breakdown on one yet so I don"t know if they can be built from another type of IH/GE Electrall. Anyway, they shouldn"t be worth much. Maybe $500.