Walmart offers the Jumbo-Tainer 7-Gallon Water Bottle, model no. 8930-03, for $17.99. (Amazon charges the same with free shipping for Prime members.) Opt for in-store pickup to dodge the $4.97 shipping fee. That's the lowest price we could find by $7, outside of the mention below. It's BPA free and features a vent cap, hideaway spigot, and dual handles.
A close price: RedsGear.com via Newegg offers it for $19.20 with free shipping.