ChubbiesTech via eBay offers the refurbished Unlocked Apple iPhone 4S 16GB Worldphone for GSM Networks in Black, model no. MD234LL/A, for $249.95 with free shipping. That's $16 under our mention of a refurb from three weeks ago and the lowest total price we've seen for an unlocked 16GB iPhone 4S. (It's also $60 under the best price we could find for a new unit.) It's compatible with GSM networks such as AT&T, T-Mobile, and Vodafone; it can't be used with CDMA networks such as Verizon or Sprint.
Note: No warranty information is provided.