Amazon offers the OxiClean Versatile Stain Remover 7.22-lb. Box for $9.99. Add it to your cart via Subscribe & Save and it drops to $9.49 with free shipping. That's about a buck under what you'd pay at a local store, although most places charge at least $19. It's meant for regular and high efficiency washers.
Be sure to cancel Subscribe & Save after your order ships or you'll be billed for subsequent shipments.