For Prime members only, Amazon offers the Learning Resources STEM Force & Motion Activity Set for $7.98 with free shipping. (Toys"R"Us charges the same via in-store pickup.) That's the lowest price we could find by $11. It includes two cars, two double-sided tracks, four weighted blocks, pendulum ball, ladder with two removable bars, and an activity guide.

Update: It's now out of stock at Amazon; however, Toys "R" Us still offers it for $7.98 with in-store pickup.