For first-time customers, Gillette On Demand offers the 4-count Fusion ProShield Razor Blade Cartridges + Handle Included for $10 after adding to your cart and applying promo code BLADES50. Shipping is free.
Also, you can place a 4-count Gillette5 Razor Blade Cartridges + Handle Included or a 4-count Mach3 Razor Blade Cartridges + Handle Included into your cart on the same order for an additional $7 after automatic $3 new-customer discount. Shipping remains free. (Note that the Gillette5 cartridge fits the Fusion handle.)