Unless I'm mistaken, which has been known to happen now and then, tractors are not commodities. The dealer buys the tractor from the manufacturer at what he hopes is a good price, then tries to sell it for a profit.
The dealer cost of the tractor sitting on the lot is fixed, not floating like the price of fuel in a tank. The price you pay is a reflection of what the dealer paid or agreed to pay the manufacturer for the unit, which may vary from time to time.