With orders of $25 or more, Swift Buy via Amazon offers Prime members the Magic Water Balloons 110-Count 3-Pack (330 in total) for $6.29 with free shipping. (Non-members can spend $49 to bag free shipping.) At 2 cents per balloon, this is by far the best per-unit price we’ve ever seen. (We saw 110 for just a buck less last August.) It’s a current low by $5. These balloons are self-tying.

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