About how much does it cost to get a iphone 5 unlocked?

I'm buying a used iphone 5 with a at&t company which I'm trying to get it unlocked so I can go with virgin mobile

It depends where you go really, just look around.

It depends on who you get to do so.

AT&T could do it, but I think certain circumstances apply
Chronic Unlocks could as well. Google them.