Originally Posted by wouter112

Cost and performance really depends on the type of traffic you buy. There are many variables you need to consider before you buy traffic. Country, type of traffic (banners, pop, redirect), devices etc.
You say you have the monetization in place, but you should know that each type of traffic needs a 'special treatment' you can push all your traffic to just one single offer, but it's better to optimize this.

Where to buy?
You should run several tests with the known adnetworks. I cannot point out one adnetwork, because they all have different strenghts. So first get your need in place en then check out which adnetwork suits the best.

If it comes down to monetization, let me know! ;-)