Lowe's has the Kobalt Garage Storage System Wood Work Surface Top for $7.49
through 10/18/17 (save 75%). YMMV.
I also found it at other locations for $11.99 through 10/18/17 (save 60%).
Save even more with a promo code, military discount, or mover's coupon.
High-density MDF durable wood surface
Conveniently standard with ruler and meter angle guide
Fits perfectly on Kobalt garage tool bases
For use with Kobalt 1-drawer 2-door cabinet
27-in W x 18-in D work surface
Easily use and convenient
Edit: If you choose a store that DOESN'T have the work surface in stock, parcel shipping is available (and free for MyLowe's members). FREE SHIPPING!
Credit to rogunit
for the tip, see below!