Amazon offers the Crest 3D White Professional Effects Whitestrips Luxe 20-Treatment Kit for $35.99. Clip the $7 off coupon on the product page to cut it to $28.99. Plus, Prime members receive free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $5.10.) That's the lowest total price we could find for this quantity by $7, although it was $1 less in December. This kit includes 40 Professional Effects strips (20 treatments).