95 Cirrus, Engine Gone?

I have a well maintained 95 cirrus v6, 110k. It has always had trouble starting when it is extremely cold. This is usually due to the battery being dead. It has a history of battery and mystery electric problems that often resolve themselves. Over the holidays it sat for a couple days and the battery drained so I charged it up and started the car. When it started, the engine was very LOUD. My reaction was to turn the car off immediately. There were NO previous signs of trouble with the car whatsoever (I had just changed fluids and drove it home from college 100 miles w/out anything unusual). I check my fluids, plugs, everything I can think of, and all is fine, so hoping it was a fluke because of the cold (it was well below zero that night) I go to start it again but no luck. It is trying but the engine doesnt turn like the charge is too low. I charge it and keep trying, finnally it starts but is still loud. Having no choice but to drive it (i had to go to work) noticed it was having a great deal of trouble accelerating. I got on the highway and finally get it up to 70, drive for 20 minutes, and it dies instantly. it wouldnt even turn upon trying to start, but the batter seemed low because all electric related devices were very weak.

The mechanics first told me that it was the starter (this confused me but i was releived), then called back shortly after and tell me my engine is gone but could not offer an explanation or even what the problem was specificially (they only said that there didnt seem to be a reason). I've been ripped off before by mechanics who claimed to fix something only to discover later that it was something else and fix it myself so I'm not totally convinced here. Sure it makes sense but this problem seems unusual and given the circumstances, I thought I'd run it by on this board and see what some of you might have to say about it before I junk it. If you can think of any alternitive explanations that I could investigate that would be nice since I can't afford to replace the engine or buy a new car at the moment.

thanks