Server Advertisement Questions!

Hello, I currently own a semi-popular and by that i mean anywhere from 9-50 players on at a time however i want to know how to maximize this.I have looked in to paid advertisements and would like to know what exactly are the best sites for this. Keeping in mind i have a budget of about 100$ and i know this price won't compete on some sites but im hoping to find at least one through the PMC community.