You could try Zillow.com, a relatively new website that somehow gives
estimates on houses throughout USA. It also shows prices on recent
Try it out. Once you have gotten a photomap for an area of Columbus,
you can click on recent sales, and then move the map, seeing adjacent
areas. The half million $ homes will obviously be congregated in the
When you open the page for more information about a house, I believe
that you will also get a statistic showing in percentages how many
homes are more and are less expensive.
Of course, this is not a direct number answer to your question, and
you probably don't want to fly all over the place counting homes.
This site suggests that there were very few such homes in 2000:
If you click on "Columbus, OH residents, houses, and apartments details"
below the level of the map, you will find a great deal more
information on housing. Perhaps you can extrapolate the information
you need from these two sites.
Good luck, Myoarin