Just thinking about how to build a GMLAN module for the h/u RGB input - it probably wouldn't need much in terms of hardware, maybe a 28 pin PIC18F2480 with the CAN protocol engine built in, a TH8056 or similar single wire CAN transceiver, 78L05 5v regulator, XTAL etc. Parts all up would probably be around $10-20ish
I bet that is about all you get in those $400 modules for disabling the VIM or enabling the camera input...