Both eBay and Amazon.com sell used mini bikes for less than $100. A used 20-inch Razor high-roller BMX/freestyle bike costs about $76 at Amazon.com as of 2015, while a used kids' Raleigh BMX cycle costs about $55.
A used 20-inch blue Mongoose boy's strike BMX bike costs about $93, while a unisex Royal kids freestyle BMX bike, available in different colors and sizes, costs about $67 at Amazon.com. Available sizes include 12 inches, 14 inches, 16 inches and 18 inches.
Amazon.com has different discounts for different models and styles of BMX bikes and offers free shipping for purchases above $35.