Joel, Bob - thanks for the deatils. the hw you have pointed to looks impressive, but is way too expensive for what i have in mind.
Let me elaborate, i am looking for something very simple like a 2 relay device which can be controlled over wireless directly by mango. someting < $30. Looking at the links you have posted and also my own googling, this seems highly unlikely.
this triggers an idea which i want to bounce off you. Using Arduino and the Rf modules which come for it, do you think it is a practical possibility to implement the MODBUS serial protocol over wireless using nRF24L01 modules and arduino MCU? I wanted your opinion on the praticality before i start investing some time in taking this forward.