Publishers want to get paid for the opportunity (CPM) but Advertisers want to pay a portion of their revenue (PPA): PPL, PPV, PPC and PPM are all proxies for th

Publishers want to get paid for the opportunity (CPM) but Advertisers want to pay a portion of their revenue (PPA): PPL, PPV, PPC and PPM are all proxies for that customer acquisition, so if you want to buy effectively, you need to start by figuring out what your costs per acquisition are. If you can't even hypothetically afford anything close to $17/lead, you might not be able to purchase customers yet, but if you can, then figuring out your lead-to-sales ratio is a lot easier than working out everything between the impression and the sales. You might consider looking for an agency that specialises in PPL/PPA; basically doing revshare, and letting them build appropriate site lists, and user demographics, and copy testing and so on to help figure out what makes your product sell -- they will put skin in the game because they can leverage their expertise.