YouBuyRite via eBay offers the refurbished Unlocked Apple iPhone 4S 16GB Worldphone for GSM Networks in Black, model no. MD234LL/A, for $259.95 with free shipping. That's the second lowest total price we've seen for an unlocked 16GB iPhone 4S; we saw a refurb for $10 less last week. (It's also $70 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.