Based on what?
Top quality sites go to brokers. Mid quality sites are increasingly being sold in places like forums and privately and via brokers. Flippa's has a lot of the low quality, template type sites and has an average sale price of around $1,000 but there are many places to sell sites like those.
Flippa is the largest single auction site, yes, but in dollar terms it accounts for less than 1% of the websites that get sold around the world every year.