With orders of $25 or more, Amazon offers its Prime members the B. Skipping Stones Toy, model no. 68690AM, for $2.38 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $14.56.) That's the lowest total price we could find by $15. They are stackable on a yellow pole (not seen in the picture).
Note that this item is part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.