Those prices are probably higher than what most would pay for a domain though, keep in mind it dose not take stuff like actual human popularity of the site, since this require inside information from you, Alexa and GPR is not enough to calculate the actual value.
such as my site(thorerik.net) is bearly worth 515$ but even that is too high, due to the special domain name

ps.
Alexa is not a suitable statistics source, since it only rely on IE users who got their Alexa toolbar, for example, among my users there is bearly 20 IE users who regulary visits, out of them, NONE uses it.

how it dose it is one thing, but how accurate is still wearry off, since it miss one aspect that only humans can see, that’s beeing human vs. a computer.
It can be used as a guiding.
proof, try google for example they suggest that google.com is worth $2,030,000,000 a fair price.
Now go on the stock market, they ended up at 576.30 in the US with over 4 million stocks, that makes rougly $2 305 200 000 as you can see the prices are way off, and this is the net worth after a down on the stock market.