The primary models for determining Pay-Per-Click are
Flat rate PPC :
In this type of model, both publisher and advertiser agree to a fixed amount that will be paid for each click. In most time, the publisher has a rate card for PPC plan based on different areas of their website or network. The amount varies as per the content that generally attracts more or less people.
Bid based PPC :
In this type of model, the advertiser competes with other advertisers in a private auction hosted by a publisher. The advertiser will inform publisher for the maximum amount of bid he is willing to pay.