I'm thinking that I could start a business to aggregate (collect
   together) small payments.  So, this business would have providers,
   and clients.  The providers would supply services to the clients. A
   provider would send me an email message saying "I just provided a $5
   service to your client FOOBAR".  At the end of the month, I would
   charge the client $5, and pay the provider a high percentage of that.

I think that there is already such a sevice.  It is called CheckFree.
I think they are located in Columbus, OH