The highly-rated 3M Filtrete 3US-MAX-F01 [amazon.com] ANSI 53 [nsf.org]
replacement filter for the Filtrete Maximum Under Sink Water Filtration System is on sale at Amazon for $27.51 with free shipping when choosing the Subscribe & Save option, or $26.06 with Amazon Subscribe and Save if you have 6 or more Subscribe & Save items.
AFAIK, there is not yet a cheaper aftermarket ANSI 53 [nsf.org]
filter available for the 3M Filtrete Maximum Under Sink Water Filtration System. This price is just 1 cent above the historic low for the 3M Filtrete 3US-MAX-F01 according to Camel x 3.
Note: There is also a 3M Filtrete system with a dedicated faucet that uses a different [amazon.com]
filter. This isn't that filter. Make sure this fits your 3M Filtrete system before ordering.