Guarantee Cellular via eBay offers the refurbished OtterBox Commuter Case for Samsung Galaxy S4 in Black, model no. 77-28769, for $6.99 with free shipping. That's $3 under our March mention of a new unit and the lowest total price we've seen. (It's a current low by $2 for a refurb.) It features an inner layer of shock absorbent protection.
No warranty information is provided.