Amazon offers the 3M Aqua-Pure Replacement Water Filter, model no. AP810, for $18.92 with free shipping when you order via Subscribe & Save. That's the lowest total price we could find by $16, although it was $3 less a year ago. It filters 20 to 28 gallons per minute and provides fine sediment filtration down to 5 micron.
Note: Be sure to cancel Subscribe & Save after your item ships to avoid being billed for future shipments.