Facebook gives you a recomended price when it comes what to pay the that i use is to first try half that price and see the results you get, and then somewhere in the middle of the two figures that you have and see what results are better for example if facebook wants
I once advertise my site on facebook, although it's not my site directly. I first build a fanpage and refer them to my site every time I make a post on my blog.
I am promote my website on Facebook. I get totally organic traffic from Facebook. I am never buy any paid service and advertisement on Facebook, But Current my website get 200 - 250 visitor daily from this website. or I get organic 200-250 traffic on my website from Facebook.
I make fan pages with main word header and then stuff them with choices the page is at the top of the search when people .
I have created a fan page for my site and invited people to join. I share news and updates of my site here in this page. So in a sense, yes, I advertise my site in FB.