TomTop offers this Large Microfiber Cleaning Cloth in Yellow for $7.99. Coupon code "AK3726" cuts that price to $5.99. With free shipping, that's $5 off, and the lowest price we could find. It measures 36" x 22".

Note: this item ships from China and may take four to six weeks to arrive.

Update: The coupon no longer applies; however, the price has dropped to $5.99.