If you (well, the purchaser) goes to a Deputy Regristrar office, they can obtain a temprary tag valid for thirty days for a nominal fee (apparently around $20). As others have said, this is really the responsibility of the buyer; your responsibility ends when you accept the money and give them the bill of sale, title, etc. and remove your plates.
Calling the BMV and asking should help you get a handle on the exact paperwork and procedure required.
I would not drive a vehicle without a registration of some sort. While it may be possible to get away with it most of the time, it is not legal in most states and the fines and hassle (impoundment, etc.) do not seem to me to be worth the risk.
