LimeSDR funded, some hours left to still get a discounted SDR
crowdsupply.com
crowdsupply.com
More to be read about technology: http://rtlsdr.org/
One of the SDR portals: http://www.rtl-sdr.com/
You can buy cheapest SDR for 20USD these days. Great to play, and there is even a marvelous GNU Radio available (http://gnuradio.org/) - Yikes :)
By the way, these are receivers. If you want to transmit using SDR, the hardware is going to be a bit more expensive.
Anything with RTL2832U + R820T will do.
Some hours and then several months.