Is there a away to transmit sensor signal over RF without Arduino?
You don't have to use a $30 Arduino. You can make a "breadboard" one for a few dollars, like this:



$5 for the chip and a couple of dollars for a couple of capacitors and resistors.



Add to that a NRF24L01 transceiver like this:



Available from eBay for around $1 each. You need two, as you need to transmit from one and receive from another.

So the whole thing could be done for under $10.




  Something that could work for considerable duration with a small tablet like battery?


See Power saving techniques for microprocessors