ExtremeSaleen

I've been having some really weird issues lately, and I'm starting to suspect the computer. Was wondering if anyone has seen this before.

Symptoms are:
1. tach goes away and the mileage display goes to just dashes while the car is running. Shut if off and fire it back up and its working again.
2. speedometer will some times quit working. Same fix as above.
3. the car stalls a lot, but fires right back up
4. Get the check engine light a lot with a lot of weird codes, like the fuel sensor voltage, coils not working, EGR errors, DPFE not reading right, just all over the spectrum. (I clear them they don't come back, just a new one pops up).
5. Car is sometimes getting about 100 miles to a tank but that varies big time. Sometime 1/4 tank for 20 miles. Sometimes it seem completely normal.

If it is the ECM or sounds like it could be, how much does it cost to buy a new one, have replaced, etc.?

Thanks for any help or advise.