Amazon offers Prime members the Magformers Magnets in Motion 32-Piece Set, model no. 63202, for $23.32 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $6.45; Walmart charges the same.) That's the lowest total price we could find by $12, outside of the mention below. This 32-piece set features ABS magnets, a crank, and spinning gears.

A close price: Target has it for an in-cart price of $24 with free shipping.

Note: It's currently on backorder, but can still be ordered at this price.