We've posted medieval manors and castles for sale on Getting Medieval. There was even a monastery. But why prattle around with that? Just buy the whole darned village and be the head honcho of your fiefdom.
This one's in Italy and goes for a steal at 485,000 pounds. Just go here for the particulars.
In 2009, there was a village in England for sale for 22 million pounds. Too bad I missed that one. I'd much rather live in England than Italy. No offence, Italia.