When people post sites for sale in the sitepoint.com forums, to prevent the general public from stumbling across the sale, they usually use a tinyURL pointing to the site and avoid using the site name in the description text. This prevents the sale post from appearing in most search results. You could also check out the robots.txt for wherever you list.
Would someone sell a site for this kind of money on Sitepoint? I've seen $15k-$30k on there, but not an amount as high as this. A quick glance is that even in the 'premium' category most are in this ballpark or less Edit: sorry, don't mean to offend. Just curious if you know of any that have sold for this amount
Here are a few that are in similar ranges:
http://marketplace.sitepoint.com/auctions/34096
http://marketplace.sitepoint.com/auctions/34080
Having tracked the marketplace for the last few months there are a fairly regular stream of companies that have $10-15k in revenue.
They tend to be forums and have a very webmaster skew. So I am not sure there would be software buyers but it's worth a shot.
This forum was recently sold on sitepoint i believe too: http://v7n.com/