Alexa is not the only parameter to judge the value of any site. There are certain parameters on which the value of the site is based on like the age of the domain, monthly/yearly income from the site, theme of the site, and also traffic of the site. Hope this helps.
i'd say it gets 50,000 - 100,000 page views a day to have that alexa rank. If you can get $3 at minimum per 1000 page views, you're looking at $400k + a month earnings. if stable, you could easily get $4 million + for a site like that.
I know a service that can bring your alexa below 1000 for just a few hundred dollars, but then would be people be interested in buying your website? Alexa is not always counted, it is the earnings that counts first.