Tractor #851 worth

The value of "Tractor #851" depends entirely on what you mean by it, as the search returned several different items. If you are referring to the LEGO Technic set, it has a used value of $132.13 and a new value of $633.16 [1]. If you are referring to the LEGO Tractor (851-1), it is currently unpriced in the catalog [4]. If you meant a tractor part, the catalog lists various items with "851" in the description, such as an Arko Light Switch for $13 new [2], a Water Pump for $65 new [3], or a Sunex Tractor Seat for $127 new [6].