Two LG Slide TU/CU720 phones - $60

These two phones were previously used on the Rogers GSM network in Canada, so they will be suitable for any GSM network here in the U.S (AT&T or T-Mobile). The phones weren't used for very long, so they are still in great shape with little wear and tear.

Both phones are still locked, but unlocking costs very little ($10-15) and is easy to do. Here are a couple of links with prices and how-to videos:
http://www.unlockallcellular.com/tu720-shine-unlock-code-np-58771.html
http://www.youtube.com/watch?v=N0sO4AIY5jU

Google Shopping tells me these phones are going for $80-100, so I'm thinking $60 for two locked phones plus the cost to unlock them is about the cost of one phone online.