More and More Car Trouble?

I have a 2004 Chevy Cavalier. About three weeks ago I was driving down the road when all of a sudden my car started misfiring. Not sure what the problem was, I got it to a mechanic the very next day. He told me it was the coil tower and it needed to be replaced. I found this odd because I just replaced that part back in February but I went ahead and did it. It continued to misfire and I kept taking it back. The mechanic told me the problem would clear up on its own. Last Friday, I was driving down the road and the car started making a strange sound and began stalling out while I was driving down the road. I had a different mechanic look at it first thing on Tuesday morning. One of my sparkplugs had exploded and blown a cylinder. So he put an insert into the cylinder and that seems to be holding just fine. However, it was still misfiring. He went ahead and replaced the coil tower without talking to me. When he told me, I told him that I already knew that wasn't the problem; it has been changed twice now over the last six months. He told me that either the car has an engine problem or an electrical one. Currently when driven, the car will misfire to varying degress, shudder a little bit while driving, and cause the check engine light to come on. These problems are intermittent and sometimes stop for a few days. Currently it is not dying while driving. He also told me he has no idea what could possibly be causing the problem. He wants 800 dollars to take my engine apart and look around so that then he can tell me what's wrong. I feel hesitant because I don't feel like he's telling me the whole story. I also asked him how much it would cost to rip this engine out and replace it. That was about 3000 dollars. Does this sound like an engine problem or electrical? My ex's good friend is an electrical wiz with cars (it's all his shop does, my ex and I are good friends) so I have someone who could find the problem if it is electrical (since I know a lot of regular mechanics really aren't so good with that). But I don't want to waste more money and time if the problem probably really is the engine. In normal circumstances, given how much this car is worth, I probably would junk it (which is probably what some of you are thinking right now) but I still owe another 7800 dollars on her. Also, I do have a friend who owns a used car dealership who would sell me a car at cost with a warranty (probably around 3500 dollars there). What direction do I go? I have to have a car to keep my job as I am a group home manager and need to be able to get here relatively quickly should an emergency come up. Otherwise I'd probably start riding the bus. Please, any good input would be greatly appreciated.