Battery light comes on and then goes off while driving sometimes

Over the last couple of years I have noticed a quick blink of the battery light coming on and just as quick turning off so fast I would be like did I imagine that? It would only happen about once every couple of months. Over the last 2 weeks it has been coming on a lot now and staying on a little bit longer as time progresses. But always turns off after about 3-5 seconds or so. I took it into a local shop who states battery and alternator is fine and say they need to check the electrical system for $100 to see if it is anything there. I have put a lot of money into this car, but is this something I am going to be able to afford to fix/worth fixing? Any ideas what this could be? I haven't driven it much since this has been progressing I am afraid to get stranded while driving.