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search for "ACTRON" on fleEBAY or try AUTOZONE, you will get a good one for under $100, your other choice is an ALDL USB cable and a laptop with something like tunerpro RT, google aldl usb.
If you just want to read error codes - most people that I know just ground the "G" pin on the ALDL connector, and read the codes that display on the speedo. No scan tool required for the OBD I system.
Some 1994's upgraded to the OBDII connector - but it's still a OBDI system behind it.
There is a good description on Zip Corvette's website (under tech).
If you want to log data - there are several options. You'll need a special cable (try ALDLCable.com) and Special Software (try Datamaster).
Do an app search for your Cell. Seems to be a lot out there for newer (OBD2) with Code Readers free, though you'll need a cable which they hock with the Apps I've seen.