Get 2 packs of Crest 3D White Whitestrips, Professional Effects (20 treatments) that drop from $54.99 to $39.99 each to bring your subtotal to $78.98 and then use this $15 mail-in rebate to drop the net price down to $63.98 at Drugstore.com. Even better use this $10 mail-in rebate to drop the net price again to $53.98 . That breaks down to $26.99 per case and the makes it the best price we could find for 2 packs by $8 (Amazon, only has 15 left in stock at the next lowest price before the price jumps to $34.54 per pack elsewhere). You'll get 40, enamel-safe teeth whitening treatments and the shipping is free. Sales tax is charged in most states.