13 Deals offers the Bigfoot 2-in-1 Small Yard Bag for $19.99 with free shipping. That's the lowest total price we could find by $7, although we saw it for a buck less three days ago (since expired.) It can be used as a tarp or as a utility bag. It measures 57" x 52" unfolded and features 5.1 cubic feet of space as a bag.
Looking for a larger size? Kotula's offers it in Large for $29.99 with free shipping. That's $4 below our expired mention from three days ago and the lowest total price we could find now by $5. It measures 118" x 96" unfolded and features 37.3 cubic feet of space as a bag.