It is not possible to accurately determine what the actual traffic is of a website with any Alexa score let alone how much specific site could mate if it’s ranked around 500000. Unless you are able to interview the owner of the website and have them tell you exactly what their traffic really is, how much they earn and what ways do they use to monetize their site. There are just so many unknown “x” variables that you need to know specifically so that you can put a math into good use. Quality of traffic is crucial here, and speaking of it and based on my personal experience I would warmly suggest Babylon Traffic if you are in dire need of traffic or you simply need a little positive boost of your monthly online metrics. Also, don’t forget that Alexa only ranks sites, it has nothing to do with revenues or how much certain websites make. To properly monetize your website you need to put ads on it. Specific kind of monetization also play a role into a correct calculation. Is it pay per view, cost per impression, banner ads or something else?
Internet traffic reporting services, paid and unpaid, are not accurate. They are based on estimates. You have to take what they tell you with a huge grain of salt. Alexa has an excellent reputation, but what they report can only be a guide.
What is clear, is that any website with an Alexa ranking of 1000 or lower is a very, very popular and influential website. It would be reasonable to assume they have thousands of unique visitors a day. The keyword is assumed.
To get a more accurate determination, it would be worth examining at least 5 other websites with comparable rankings in the same niche. Checking their Alexa rankings, as well as their position in the top ten results of the major search engines.