Wow, according to that formula, I could sell my site for $300,000! Time to cash out. http://www.very-cool-stuff.com/ubb/smile.gif
Realistically, when you sell a web site it is a bit like real estate. The thing that should affect the price the most is "cash flow", or how much the site is making in revenue. Also, potential revenue could play a part if someone believes they can improve the revenue of the site with more exposure etc.
Overall, I haven't seen any exact formula, it all depends on the market for the product. If someone wants it, it will probably be sold. http://www.very-cool-stuff.com/ubb/smile.gif