Amazon offers its Prime members the Uncle Milton Vintage Ant Farm, model no. UM0017, for $4.99 with free shipping. (Non-members can spend $25 to qualify for free shipping; otherwise it adds $4.67.) That's the lowest total price we could find by $15. Sales tax is added where applicable. This kit includes sand, tubing, a mail-in coupon for live ants, and ant watcher's manual.

Update: The price has since increased to $5.99 with free shipping via Prime. That's still a price low by $14.