Yeah, finding good parts can be a drag, but I've so far been blessed with good retailers around here. Good support for old-ish bikes.
But for real, before getting into bikes I would have said an 80's bike was "old". Now I say if it's in good condition, get one. You're getting some great value for the price. I paid $1000 tops for my GPz, and it used to be a superb race bike back in the day. Still feels like it, too.
I might be getting something more modern down the line just for the electronics, but if you're on a budget, an 80's bike is an awesome choice.