Cavalier battery problem.I think

My 1996 cavalier wouldn't start the other day. I turned the key in the ignition and there was nothing. No clicking, etc, just completely dead--car won't start, no lights, radio. No problems before this happened. I discovered I could tap on the battery posts with a wrench and then it would start. Now I go through this routine every time I want to start the car. Do I need a new battery? Alternator? Clean the cables? Not sure what to do and I certainly don't want to put much money into it and I'm trying to get a little more out of it before I get rid of it. Thank you!