You can buy the springs at Home Depot, just make sure you get the right one and be careful with install, one slip and you have a very messy injury to deal with.
It is always a good idea to lubricate those springs, helps stop them from rusting and thus weakening to the point where they break. You can buy a spray, or get dirty with motor oil for a lot cheaper. $100 is a good price, just paid $135 to get one of the two on my door fixed. PIA DYI job if you don't know what you are doing. If you live near a subdivision that still has homes under construction, stop in and ask the superintendent for a lead. They are generally nice guys who will hook you up with one of their vendors workers that might do it on the side after work for a real good cash price.