QualityZoneOnline via eBay offers the Bobble 18.5-oz. Filtered Water Bottle
in Yellow for $2.43
with free shipping.
(It's available in five other colors for pennies more.) That's a buck under our mention from last December and the lowest total price we could find now by $6. It features a replaceable filter.
Note: It ships from China and may take three to eight weeks for delivery.