Amazon has the Amazon Basics 3-Blade Motion Sphere Razor w/ 20 Blade Cartridges on sale for $12.37 - 5% off with Subscribe & Save (can cancel anytime) = $11.75 with free shipping on $35+ or with Prime. That's less than 60 cents per cartridge. 

• The 12-Pack of Cartridges is $7.60 after S&S (63 cents per cartridge)