The Best Buy buyback idea seems to have some merit. In theory you could get ~$225 back on your Pre 2 ($125 after you pay the $100 buyback fee).

One thing that comes to mind is the fact that BB doesn't seem to sell many unlocked smartphones. Perhaps it is just their horrible website, but it looks like you have a diminished selection compared to the carrier plan phones.

Still would be ~$525+ in a best case scenario, which sucks (plus that buyback money is a bestbuy gift card). Better than $650+ though.