PayPage is a system, seaming to appeal to the giant userbase of Amazon, mainly (but not restricted to) bibliophiles.

http://s1.amazon.com/exec/varzea/subst/fx/help/payor-faq.html/ref=zm_pb_h_04/104-1449896-3794364#what-is-this

Are there Wikis with a (voluntary) PayPerView mechanism to test?