With orders of $25 or more, Amazon offers Prime members the Crayola Window Markers with Crystal Effects 8-Pack for $2 with free shipping. (Non-members can spend $35 to qualify for free shipping.) That's $2 less than what you'd expect to pay in your local store. It includes eight non-toxic markers in assorted colors.
Note: This item is part of Amazon's add-on program and can only be purchased with an order of $25 or more.