DARPA is funding RASCAL development
Or is it ARPA once again. Anyway, it seems that the funding is coming from the DoD, not the private sector.
If the supersonic booster was being built in a conventional manner, similar to the SR-71, then I'd agree that it would cost several hundred million dollars to develop. However, discounting the engine costs (they'll probably be government furnished equipment), I'm reasonably confident that Rutan can build the basic airframe for much less. The flight profile doesn't call for long periods at high supersonic speed, so the thermal effects should be much less difficult to manage. Rutan has some good supersonic experience now and he's applying those lessons to RASCAL.
I wonder if RASCAL will have a shuttlecock mode.