Express Water via eBay offers the Express Water Reverse Osmosis 5-Stage Under-Sink Water Filter, model no. RO5DXC7, bundled with seven replacement filters, for $138.95 with free shipping. That's a $220 savings and the best deal we could find. It filters up to 50 gallons per day and features BPA-free parts, quick connect fittings, and a long-reach drinking faucet.