Target offers the PUR MineralClear Faucet Filter Refill 6-Pack, model no. RF-9999, for $37.99. Tick the box marked "save 5% when you subscribe" to cut it to $36.09 and bag free shipping. That's $2 under our December mention and the lowest total price we've seen. (It's a current low by $2, although most merchants charge $50 or more.) It purportedly removes lead, microbial cysts, and other contaminants from water.
Be sure to cancel your subscription at Target after the item ships; otherwise, you'll be billed for future shipments.