Amazon offers Prime members the Camelbak Antidote 70-oz. Reservoir, model no. 90762, for $15.93 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $5.58.) That's the lowest total price we could find by $6. It features an air-tight fillport, quick-snap cap, and Quick Link system to easily switch out reservoirs.

The 100-oz. reservoir is also available for $16.93 with free shipping for Prime members. That's the lowest total price we could find by $6.