My opinion is that standard project management approach, where you estimate time needed and translate to money works for bigger projects which are done via bounties - like porting Poseidon. The cost was estimated by developer, money was collected, work was done.
For paper cuts I think we should follow a simpler approach similar to @terminills is proposing:
1) Have a relatively large pool of "rather small" issues (> 100) so developers of different experience level can choose from
2) Have a fixed price per issue - yes, some issues will be harder, some easier, but keep the rules simple
3) A (theoretical) developer looks at issues, looks at price and decides if he is interested to make quick buck or not