Could be just the regulator in the alternator. Side-of-the-road-with-a-screwdriver job if you can get under the car... and have a replacement regulator.
Check Thomaspin's website for details on replacement. Do a search on any post by Thomaspin. There's a link in his sig line.
There's a good chance it will quickly go downhill once the dash lights come on. I would not try to go more than 10 miles in this condition.