Save on Expo magnetic dry erase markers with Amazon's Subscribe & Save program. The 4-pack of markers is on sale for $4.59 on Amazon and you can save an additional 5% or 10%. Your total will be as low as $4.13 for four markers. The colors included in this pack are black, blue, green, and red.
While you're here, check out this DIY way to revive dry erase markers and Sharpies.