Short answer: "It depends."
Long answer: "The value is the actual amount that you can get someone to pay for it."
Some people will tell you 1x annual revenue. Others 2x or 5x, or even 10x. Others will tell you to be happy for .5x. But none of those matter unless you find someone who will actually give you those numbers.
One question I have is why would you want to sell it if it's such a cash cow? This is not being sarcastic- that is a legitimate question that a serious buyer would ask. Not many people would be willing to sell in a situation like this, so it raises a big red flag and you'll need to have an answer that satisfies potential buyers.
because it's a pretty easy site to make.
That in itself sounds like a huge devaluation.
is it possible to sell a website subject to all the statements about the site being true with the cash held in escrow or something like that?
What are the conditions of the escrow- can the person back out once he finds out what the site actually is? If not, would YOU buy something with conditions like that? (I know I certainly wouldn't.) If so, then coupled with the previous quote, it seems like a smart would-be buyer could back out as soon as he finds out the domain name and do it himself.
Disclaimer: I have not personally been involved in the selling of a web site, but I have been in business for 15+ years and have been involved with the valuations of businesses (or portions of a business), which is really what this is. The ridiculous valuations that people have bought into usually result from investors that get snookered into thinking they're going to get an easy return on their money, when they didn't really understand the business. For people who have to actually take over the business and do the work, the valuations are more realistic because they understand (or they should understand) what's required to keep the venture going (and growing).