I’m not much of a microwave guy, but the article “Mattel makes a real radar gun, on the cheap” on RF Design Line looked intriguing to me. Designed to measure the speeds of Hot Wheels model cars zipping around a track, it emits and detects a pulsed 10.5 GHz microwave signal. It seems to me that you could buy two of them (they cost $30 each) and with a little hacking get them to send and receive CW at the very least.
The article has a lot more technical detail. Perhaps someone with more microwave experience could take a look and tell us what they think.