Amazon offers Prime members the Toy State CAT Mini Machines 5-Piece Set for $5.32 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise shipping adds $6.15.) That's a buck under our October mention and the lowest total price we could find by $8. This set includes a dump truck, bulldozer, wheel loader, backhoe, and road compactor.

Update: The price has dropped to $5.10.