Dan has previously stated that VRD should run under VMware Fusion, but it's not supported. Fusion 4 is cheap because it's now licensed per household not per computer.
So you might try that route. Then in order to be legal you need a version of Windows. But you might already own an old "retail" one, which you could use. You might not legally be able to use some "OEM" type Windows licenses except on the computer they were originally licensed on.
VRD purportedly runs
under Windows XP, so you might be able to pick up a cheap copy of an older version of the Winblows OS on somewhere like fleabay.