The value of your website is what a willing buyer will pay for it. No more, no less. Depending on which website value calculator I use, my website is worth anything from ZERO to $15,000. Basically proves that website value calculators are WORTHLESS.
The value of website depends on the strategies of marketing. When you know the rule, you see the big result.
A general rule of thumb for me is 8x monthly profit (w/ advertising expenses factored in). Some people say 10 months, others 12. I think 8 is about right.
There are a lot of factors to consider. Number one of course is the traffic. But before that you have to take note the design, content, usability, and functionality.
The ONLY thing that matters is whether it is making money. If if is NOT making any money, it is WORTHLESS. It does not matter how pretty it is, how usable it is, how much content it has, what kind of design it has, nor any other superficial factor, IF IT DOES NOT MAKE MONEY IT IS WORTHLESS.