Module that allows users to pay each other ?


I am building a website where a core function is that users can post something that shows up as a node. Users of a different class (user b) can see those and then reply with a monetary offer. The original user can review multiple offers and accept one in which a payment is made from the original used to user b. 

I was was wondering if there are any modules that would make this easier to make before I try to struggle and figure this out the hard way.