Amazon offers Prime members the Crest 3D White Whitestrips Luxe with Advanced Seal Technology 14-Treatment Kit (pictured) for $27.99. Clip the $7 off coupon on the product page to drop the price to $20.99 at final checkout. With free shipping, that's the lowest total price we could find by $5. (Non-members can spend $35 or more to qualify for free shipping, otherwise shipping costs $5.01.) The kit includes 28 strips (14 top and 14 bottom).

Also available is the Crest 3D White Professional Effects Plus 1 Hour Express Whitening Treatment 22-Treatment Kit for $43.99. Clip the $7 off coupon on the product page and checkout via Subscribe & Save for a final checkout price of $34.79 with free shipping. That's a price low by $20. This kit includes 20 treatments of Professional Effects and two treatments of 1-Hour Express whitestrips.

Note: Be sure to cancel Subscribe & Save once your order ships to avoid being billed for subsequent shipments.