Target via eBay offers the Hot Wheels Mega Garage Playset for $25 with free shipping. That's the lowest total price we could find by $20. It has a working elevator, turnstile, and two car launchers; it comes with one Hot Wheels car.
Mattel takes up to 65% off almost 200 items as part of its Holiday Clearance Sale, with prices starting at $1.99. (Click on the "Clearance" link at the top of the page to see discounted items; prices are as marked.) That's the best sale we've seen from Mattel since May, when we saw up to 75% off with an extra 10% off. Shipping starts at $7.49, but bag free shipping on orders of $25 or more. Some best bets, both with free shipping: