Ok, I have played around with the pixel ads script and got it so that with one simple code added to your websites, your user can place an advert to appear on all of your websites! You have full control over cost per block and can use many payment gateways including Paypal. I even host the script so that you don't have to worry about server costs. If you are interested then see a demo at any of my classifeds websites in my sig links. Then post "Im Interested"