Walmart offers the LEGO Technic Class Xerion 5000 Trac Tractor for $109.61. Opt for in-store pickup to cut the price to $106.79. (Amazon charges the same with free shipping.) That's $5 less than we saw in April and the lowest price we could find by $6. This 1,977-piece kit includes a LEGO Power Functions motor and can be configured to carry out a number of motorized functions.

Update: The price has dropped to $107.99 before in-cart discount, $105.17 after. Amazon charges a buck more.