With orders of $25 or more, Amazon offers Prime members the BIC Mark-It Color Collection Fine Point Permanent Markers 12-Pack in Assorted for $3.99 with free shipping. (Non-members can spend $35 to qualify for free shipping.) That's the lowest total price we could find by $5. They feature fade-resistant, acid-free ink.
Note that this item is part of Amazon's "Add-on program" and can only be purchased with an order of $25 or more.