You are talking here about developed sites with revenue, not names only.
It is business like any other one. Thoughts here are devided about valuating such businesses, in a wide range.
You can hear that the price should be anything from two months revenue to two years revenue!
Of course, there are many other factors involved, which should be carefuly examined before final valuation, like in your case traffic deduction of other sites providing the traffic for the main site, seasonality of traffic, actuality, honesty, etc, etc.