You're asking the wrong question....
How must is this site worth? ---- Wrong question
How much is this site worth to "me"? ---- Correct question
That is very true, but equally you need to have a dose of reality - especially if you're making quite a bit of money with the site as it can cause drastic differences in the valuation.
When I was first approached about the sale, I thought - yeah, I'd sell for £1 million! When I worked out how long it would take for the purchaser to earn that back, let alone make any money on it, it turned out to be over 20 years! Not practical. My case was simple in the end, we needed enough to be debt free as it would take away my main income. Eventually we got to a level that achieved that - helped in no small way by the above Entrepreneur's Relief as the difference in tax was very, very large, well into 5 figures.
Quite eye opening as it happens.
- Sale as a normal business transaction & then withdrawn from the company as normal - worked out at around 70% tax
- Sale as a Captial Gain (i.e. money paid to you personally - see note above owning the domain name personally above) - around 38% tax
- Sale as a Captial Gain under Entreprenure's relief 10% tax
to give an example of a sale value of £100,000
- 70,000 tax
- 38,000 tax
- 10,000 tax.
As you can see, quite a difference.
This obviously applies to the UK only.
So, back to the quoted post - you need to have realistic expectations. No one is going to buy a site if the ROI is too long. 3 years is the norm, 5 years if you're lucky. Expect anything out of that and you'll be pricing yourself out of the market. Forums are volatile things at the end of the day, all it takes is one argument or so forth on the site and the membership can splinter off onto a new forum. Buyers obviously know this and won't tolerate long ROI periods.