HackRF One and HackRF Pro

If I was fitter I might seriously consider buying one of these. 

They work on RX and TX from VLF to 6GHz, making them ideal for experiments, especially with an external RF amp. 

Output power is in the low milliwatt range and I expect a low pass filter would need to be added for "on air" use e.g. as a beacon.

I see MLS in the UK supplies them.