Lots of warriors asking how to value their websites before selling them and it seems there is no definite answer to that question. Though I am new to WF, I've been a senior member of SP since 2004 and I thought these guides could help you guys. I've been selling websites in SP marketplace before Flippa is created and I collected some useful articles there that I check from time to time.
Here's how to estimate the value of your site.
1. The Ultimate Web Site Valuation Guide
2. What's Your Web Site Worth?
3. Determining the TRUE Value of a Web Site
4. Tool: Website Valuations and Appraisals, Value a Blog, Domain or other online Business
Hope these helps.