Amazon has Expo 2-in-1 Dry Erase Markers for $10.59 (Reg $25) with free shipping on orders over $25 or with Amazon Prime orders.
Expo 2-in-1 Dry Erase Markers have a different bold shade at each end and a chisel tip that marks three line widths. That means you can create precise lettering with one color and flip to boldly add emphasis.