Amazon.com offers the Brita On-Tap Replacement Filter
in White, model no. 42401, for $14.53
. Shipping adds $5.20
, or spend over $25 for free shipping. Even with shipping, it's the lowest total price we could find. Designed for the Brita faucet mount system, this filter lasts for approximately 100 gallons or four months, whichever comes first.
A close price: JR.com has it for $16.99 plus $2.95 for shipping.