Hello Again!

Well, my 240 is again having difficulties. When the cold weather hit last week I noticed my voltage level was low. Over the next couple days it fluctuated from low to being fine and back to low again. Finally I shut it off one day and it wouldn't start again. I took it to a mechanic and they said they tested the alternator and then the battery and it was the battery that was dead. So, I bought a new battery and of course that helped for a few days until the battery died again. I took it back and they replaced the alternator (salvaged part) and again I go to leave and it won't start. The needles are jumping all around and there the volts are at 0. I have them test the old alternator that was in the car and it was fine as well! So basically I just spent $200.00 and the problem isn't fixed. I was told this was an electrical problem and it could be a nightmare to find and to fix. This car is very rusted underneath due to being an upstate ny car... also, I bought it for 800.00$ and have had to spend at least that much fixing it since I've had it for 4 months. This car is a nightmare and it's breaking my heart!

Anyone have any advice? I just honestly want to get rid of the car but I can't really sell it if it won't start. It has 135k miles and the body is rather unattractive. The inside isn't much better!

-Thanks!