How to put a valuation on a website idea?

Thanks EcommConsultant - have worked up those models using different "average cost per acquisition" of Users. A question: is there an "industry average" for cpa? (digital industry).

Or are there some "typical" cpa costs for various sectors? Social networking and gaming/gambling being the most relevant to my plan.

I know there are headline deals for "sale" prices too (the famous ones such as myspace etc) but again i wondered if there are any yardsticks that are used for "buying company" metrics related to the user base?

Comments welocmed thaks

Dave