1997 Ford Probe New battery still dies.

I've been driving this car for about a year now. Off and on between me and my dad and it's mine now.

There have been two different batteries in this car that I know of, both of them used.

The last battery worked off and on, and more times than not we'd have to bump start the car even after driving around for hours.

After charging overnight, the battery was completely dead. The radio screen barely lit up, and the horn wouldn't work.

I purchased a brand new battery from NAPA auto for about $80 which worked for about two days.

It powered my laptop the whole time, going 10 hours without starting the car up, no problems.

And today I had to bump start it again a few times.
Just now I tried to start it up, and it made an unusual clicking noise.

Guessing by the hit/miss of it all, I'd say there was a wire loose somewhere. Just need to figure out where. I would probably be better off replacing all of the vital cables in the engine because of all of the wear and corrosion. But how difficult would something like that be? And how expensive? Where do I start?