I found one on eBay. Just look up ford contour/mercury cougar alternator. Last time I looked, it was like $25. Only problem is it isn't guaranteed without any warranty. You may just want to take a look at the regulator assembly itself. Your problem should be somewhere in there since you said when you accelerate your battery light goes off. If the voltage is progressive (meaning it gets higher as the revs increase), your alternator is fine and just the regulator has gone bad. Sorry if I'm repeating myself. I typed that other stuff when I woke up this morning!
Sean
