Okay, assuming it is indeed 'trivial', I'd be interested in funding a build of this idea on top of a StatusNet (identi.ca) base as a proof of concept.
If any php developers out there want to take a stab at it, post your price here.
When you're done it should include:
1. user A pays user B to follow user A, based on a either i) a price set by user B, or ii) an offer made by user A and agreed to by user B
2. user A charges user B to follow user A, based on a price set by user A
3. user A can tip user B for a particularly brilliant tweet