Amazon has the 18-count Purina DentaLife Large Dog Dental Chewson on sale for $8.97- 5% off with Subscribe & Save (can cancel anytime) - $2.69 off at checkout = $5.83 with free shipping on $25+ or with Prime. YMMV: Select accounts may have additional 15% off coupon. 

In addition, the 58-count bag (Mini) is $4.70 after S&S and coupon.