Ask HN: Advice for Payment Processing?

I need some advice for setting up payment processing.. I know it's been discussed extensively around here but it seems like our use case might be slightly different than other typical web apps, either requiring an extra step or different solution than the average e-commerce transaction..

The basic concept: An e-commerce site with multiple vendors showcasing their products, company will take a % of each transaction (listing fee) before sending each vendor the remaining funds. (somewhat similar payment structure to http://www.kickstarter.com/)

I am looking for the best solution to allow users to checkout on the site using a credit card - I do not like what I've seen with either Amazon Web Pay or Paypal Adaptive Payments so far.. it looks like both of these require users to be redirected to their site for secure checkout. Reading the development forums for Paypal, seems that there isn't any planned support for Website Payments Pro and Adaptive Payments together (unless I'm completely missing something).

Steps to Successful Transaction: 1. Customer visits site and makes a purchase using their credit card (without leaving our site) 2. For using our site the vendor is charged a % transaction fee 3. Remaining funds after fee deductions are sent to vendor

Need to think about the best way for these transactions to happen, and also look at all of the fees involved with moving the money each time. Should funds move to vendors each time a transaction is complete? At the end of each day? Once every 30 days? Without an elegant solution it seems like this could get messy rather quickly.

Many thanks for your help!