This Crest 3D White Professional Effects Whitening Kit drops from $54.99 to $35.99 to $20.99 with this $15 mail-in rebate at Drugstore.com. Plus, new customers can use this link to drop it to $15.99. On top of that, shipping is free. This is the lowest price we found for this popular teeth whitening kit by over $15. It's designed to be used over 20 days and has 4 out of 5 stars by 137 Drugstore.com reviewers. There is no sales tax (except IL, NJ, NY and WA).