This is an excellent question.
There is a difference in price between selling a single site and selling an adult business.
Free sites like TGPs, MGPs, etc. are seen as commodities. These sites sold individually garner a much lower factoring rate. It is sold at a discounted replacement rate (cost of building a new site from scratch). The source of traffic after the sale is also critical if the free site loses that source. Sale price in this case is based on traffic and revenue without the "network boost."
3-6 times monthly revenue.
Ex:
www.tgp.com has 50k a day, one year old, $2000 a month in revenue (steady), $500 a month in expenses. Selling price: $3000-$12,000.
There is a big difference of who buys the site. If Drinking Hard of GTS were to buy the TGP, surely the price could be higher because of the ability to extract greater revenues than little old me.
On the other hand, selling a complete business would generate much higher factoring rates. Choker mentioned that he clears $30,000 a month for a well established business with a stable future. Coker could easily ask $360,000-$720,000 for his network.
1-3 times yearly turn over.
As a public company with favorable stock market image (ex:NOOF) with a few million in assets and stable revenue, a company could generate 5-20 times sales as a purchase price.
NOOF is selling at 17 times net earnings ($150 MM market cap). I assume there are some 20 online adult companies that would qualify with this type of pricings.