How to calculate web application's price?

Hi I want to sell my site, it has only ~150 visitors daily but it sells virtual goods and raises ~$150/month. How can I calculate the total price?

First thing we need to know is how long has the website been making $150/month? the new owner will need to know before even considering buying your website.

I've launched it 1 month ago.

Can You PM Me Site URL?

Most of the time , a website worth is the monthly revenue x 12 (annual earning) .
Or you can google "Website worth" and there is few website that should calculate that based on the backlinks , shares on social media and other different factors .
However you should understand that the calculation is based on the number of visitors and ads so If you are using affiliate links and that kind of things you probably won't get how much it really worth .