The Dream II, at 6m long, 2m wide, 1.1m tall at the center, and 170kg:
There are a very small number of solar cars with lower Cd, and you could picture increasing their wheel count to 4 without too much drag, but I'll agree that we have yet to see >0.10 for a "car". For a "reasonably practical car", I still haven't seen anything less draggy than the Probe V.