With orders of $25 or more, Amazon offers Prime members the Prang Fine Line Washable Art Markers 8-Pack
with free shipping
. (Non-members can spend $35 to qualify for free shipping.) That's the lowest total price we could find by $3. They feature 2.75mm nibs and washable 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.