What's wrong with paying by stuff that is actually downloaded rather than just looked at......
It would seem to me to be the fairest way of all to filter content.... if somethings naff then no one will download it. the biggest problem with paying by page views as far as I could tell, was that you had to look at the actual page to decide wether or not you wanted something.... most of the time I'd look and then not download said object once I'd seen a full sized preview and read the info......