Amazon has the well-reviewed 5-Pack Hot Wheels 1:64 Scale Die-Cast Toy Cars (Styles May Vary) for $4.69 with free shipping on $35+ or with Prime. Also qualifies for Save 50% on 1 when you buy 2 promo. 

Five-packs have cool themes like X-Raycers, Mud Studs, Nightburnerz or HW Getaways.