Amazon offers its Prime members the EarthEasy LifeStraw Family 1.0 Water Filter, model no. LSF101402, for $41.98 with free shipping. (Non-Prime members can spend $49 or more to qualify for free shipping; otherwise, shipping adds $5.58.) That's a buck under our mention from a month ago and the lowest total price we've seen. (It's the best deal now by $7.) 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: Note that this item is temporarily out of stock, but can still be ordered at this price for delivery when available.