If you want to save money on Apple gear, the smart money is on refurbs. Just one hitch: no iPhones. So if you want one that's used and unlocked, you typically have to look to independent sellers on eBay.
Now, and for a limited time, you can look to Apple on eBay: a non-branded (but decidedly Apple-related) Factory Outlet store has cropped up offering a handful of recertified iPhone 5 models -- at prices rarely seen elsewhere.
The selection currently includes the iPhone 5 in black or white with 16GB, 32GB, or 64GB of storage -- and priced at $449, $479, and $499. (That there's so little difference in the price means the 64GB version will undoubtedly sell out first.)
All the phones are unlocked GSM models, meaning you can take them to AT&T, T-Mobile, or just about any smaller provider which runs on the larger network (e.g., H2O Wireless, Straight Talk, etc.). My advice is to shop around for the best monthly plan, and don't get locked into a two-year contract! That's the joy of the unlocked phone!
Although there's nothing on the Factory Outlet page indicating this is an Apple joint, the exact same terms apply: full one-year warranty, like-new condition, manual and charger included, and "final quality inspection by Apple." I'm not sure why the company opted to move this inventory via eBay, but no complaints: it's highly unlikely you'll find a better iPhone 5 deal elsewhere.
Assuming you want one. The iPhone 6 is just around the corner, and $450 to 500 is still a hefty chunk of change. Your thoughts?