With orders of $25 or more, Amazon offers Prime members the Nerf Super Soaker Alphafire Blaster for $3.99 with free shipping. (Toys"R"Us has it for the same price via pickup; non-members can spend $35 to qualify for free shipping.) That's the lowest total price we could find by $8. It holds 7 oz. of water and shoots three streams.
Note: This item is part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.