Amazon offers the EarthEasy LifeStraw Family 1.0 Water Filter, model no. LSF101402, for $41.98. Plus, Prime members receive free shipping. (Non-Prime members can spend $49 or more to qualify for free shipping; otherwise, shipping adds $5.58.) That's tied with our December mention and the lowest total price we could find by $6. It filters and purifies up to 18,000 liters of water, enough to supply clean drinking water for a family of five for up to three years.
Update: It's now temporarily out of stock but still available to purchase at this price.