Amazon has the 3-Pack 3.2oz Colgate Optic White Advanced Whitening Toothpaste for $11.46. Change to quantity 2 (6-Pack Total) to reach $23 - 5% off with Subscribe & Save (can cancel at any time) - $13 off at checkout = $8.85 with free shipping on $35+ or with Prime.  Roughly $1.46 per 3.2oz tube.