1993 Subaru Legacy Issues

I've had my 1993 Subaru Legacy for about 2 years now, and it ran great when I first got it. After about 6months I started noticing that I was not getting a lot of power to my electrial instruments ( windows, radio, dash, etc), and my Rpm's would throttle every time I pressed the accelerator, even at stop lights the Rpm's would jump up to 2 or 3 for some reason. I lived with the problem thinking it was prob. just my batt. but it wasn;t because my batt. checks out good along with my alt.
Recently I took the car out of town and drove it longer then my normal commute, on the trip my car started acting crazy. While I was driving at night the dash lights started to dim until completely gone ( along with my headlights), the radio got quieter and quieter until gone. and I lost all power, then my transmission would start jerking my automatic car around like I was a newbie manual driver getting stuck in gears. Then it just simply shook like crazy and died. It won;t turn over or anything now, (although i still have batt. features like open door light etc.) I took it to an mechanic who said it might be the ECU, but thought it could be something else and needed to be able to run the codes.  I was wondering if anyone else has had issues like this that seem both electrical, and mechanical at the same time. Someone also said I could be a timing belt, but as a woman who isn't very mechanically inclined I'm lost. I don;t have the money to shell out $600 bucks for a new ECM without trying every possible resource so if anyone thinks they know what it might be, your help is greatly needed. Thanks a bunch!