Airmark via Amazon offers the Airmark Liquid Chalk Marker Pens 18-Pack for $21.95. Coupon code "MOSRGLDO" cuts them to $15.36. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $3.99.) That's $21 off and the lowest total price we could find. Each marker is non-toxic, 100% water based, and features a reversible tip. 32 reusable chalkboard labels and four replacement tips are included.