I've had a few service calls to replace door springs or cables. One time I even had to repair the ceiling and the wall where shrapnel went through. Thankfully nobody was in the garage in the middle of the night when the spring broke.
Every service call I've had done was cheap, only took a few minutes when done by a guy that does this many times a day and there was no blood spilled. Believe me, these things are dangerous if you slip while winding the spring or you don't get the cable secured properly.
Sure, you could probably do it yourself but it's kind of like home dentistry, if you get what I mean.