Where to unlock AT&T iPhone 5 Online?

I recently purchased an iPhone 5 from Craigslist, which is still locked on AT&T. For whatever reason, the owner wasn't able to get AT&T to unlock it (no, it's not stolen property), so it remains locked. The cellular repair stores in my town and nearby locations refuse to associate their business with unlocking iPhones, but I know it is possible because my iPhone 4 from last year used to be locked to AT&T and the person who sold it to me had it factory unlocked for me to use with my pre-paid T-Mobile plan! I really need my iPhone to start working again very soon, but I don't wish to pay more than $60.00 maximum for it to be unlocked. I need my iPhone unlocked because I'm off to uni in a few weeks and need it to work way before then for work and such.
Does anybody know trustworthy websites that can unlock an AT&T iPhone 5? I need it cheap, and trustworthy, so it'd be even better if you've had personal experience with the site! Also, how much time would the site take? Preferably something less than 24 hours!

Chronic Unlocks, though I'm not sure if their prices have changed since the last time I've used them.

Currently there's no 24 hour method. The fastest that I've found to actually work is 1-5 days and $150. Since you are on a prepaid plan you might as well just get one that doesn't require unlocking. AT&T GoPhone, H2O, and Red Pocket will all work with your phone and give you better coverage than T-Mobile. Their plans start at around $40 so that's way cheaper than trying to do an unlock right now.