For those who bring traffic to their affiliate sites purely with just with Adwords, I wonder how much do you spend on Adwords while you make one commission? E.g. let's say the commission amount for one referral is $65. How much do you spend on Adwords in average to get one commission - to make $65? What is your ROI? I'm not asking you what products are you promoting, I'm just trying to figure out how much should I spend on my Adwords campaign maximally.