Yes, it seems like it is always a pain to find exactly what you want. That's actually why the GEVCU hardware is custom made. We didn't find anything we really liked either. But, the good news is that you do have options. The MBED system you were looking at is very nice. We have the GEVCU hardware. I don't see any reason that you could not retrofit something from either of them. Yes, the cost of the GEVCU hardware is expensive but the design is open. You can make modifications and then build them in China as cheaply as possible. The version 6 design of GEVCU should have the capability of bluetooth and wifi as well as an SDCard. There are lots of great MBED designs you could modify as well. So, options exist. But, unfortunately you might be stuck building your own hardware to fit your needs. I'm just not sure that anything exists that matches your needs closely enough.
-Collin