A cable under tension is not a place to save money on parts. Extension-spring cables and the springs behind them store enough force to snap a broken bracket toward you, and a lot of the injuries we hear about started with someone trying to rethread a cable on a still-loaded door.
What you can safely do yourself: look at the cable for fraying before it breaks, check that the bottom brackets are tight, and clear the tracks of debris. If a cable has already let go and the door is stuck half-open, don't force the opener or pull on the door by hand. Leave it where it sits and call. It's a straightforward repair for someone who does it regularly, and the risk-to-savings math doesn't favor doing it yourself.