Last week, one of the (two) springs on our garage door broke. For those who have never heard it, it sounds like a civil war era cannon. Gave my wife quite a scare. Today during my lunch break I drove out to a supplier, paid a whisker over $100 for a new pair of springs (when one goes, the other typically is not far off), and installed both in about an hour this evening. They're the "EZ-Set" type that allow you to replace them without dealing with the danger from un-tensioning springs. (I've done the traditional kind too, and they're no big deal either)
I have no idea how much a garage door company would charge for replacing the springs, but I'm sure it's a whole lot more than the $0 I paid for my own labor.