The Telemetry Module at Hobbytown is $184. I'm not sure how many sensors that comes with. If I remember right, there are seperate sensors to read Temp, RPM, Voltage, etc. They then transmit the info back to a small Rx that you would have attached to your Transmitter, so you could look down and see the info.

On the Nomadio system, you can set up different alert tones or vibrations to alert you of problems (Excessive heat, low voltage...) I'm not sure if the Spektrum module will do the same thing.