If your cool with preset permissions, the best solution is
http://www.pay2play.com in my research. I have used them since 2006 and the payments are always on time. Cost to set up = $0. Percentage taken for processing only 5%. Check out the site for more details. Here's one of my files to see the end product:
http://vidarchives.pay2play.com/DRM0...NGURL_9368.wmv
Another cool feature is that other webmasters can "add a wrap" to a file and sell your content for you too. It's like a built in affiliate per file system and the affiliate sets their own cut. I have not really developed this side of it yet, but hope to do so this year.
Good luck!