$499 for HPTuners for 2 vehicle types. You get 2 complete model years/types for the $499. That is for their standard IO interface. You do not need the $649 Enhanced IO interface unless you plan on installing an EGT or Wide Band O2 sensor. The EIO interface just allows you to log that data with your cars ODB2 data in one software package. I purchased this version and have yet to use it.
I don't know much about EFI Live. I have heard good things about it, I do know that the guys at HPTuners will take it as a trade in towards your HPTuners purchase.
If you got someone with a Corvette close by (and I know you do ekool) who would want to go in on it with you, you could get the 2 vehicle types on one cable and share. Only one car can be tuned at a time anyway. I can also help you with tuning using your narrowband O2's.