With orders of $25 or more, Amazon offers Prime members the Rocket Balloons 40-Pack with Pump for $3.61 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it starts around $5.) That's the lowest total price we could find by $10. These balloons are meant to be inflated and then released, to zoom about the room, knocking over glasses of wine and grandmothers. (Just stop leaving your wine and grandmothers unattended, and it'll be ok, though.)

Note that this item is part of Amazon's "Add-on program", and can only be purchased with an order of $25 or more.