Just to close this thread out, I ordered the $88 OBD interface from obddiagnostics.com and tried it out in the Elise and it does work. I haven't explored all the features, but it had no trouble communicating - showed RPM's, O2 sensor output, etc.
I've used Freescan on the Esprit and this is similar, although I liked freescan's opening screen a little better. With obddiagnostics, you have to right click on any parameter you want to monitor. However, this unit does seem to have more features in menus I haven't explored yet, and best of all it will do all of my other cars.