Was thinking more towards that those farmers may contribute their 5 cents into how the milk logistics should be optimized bw/ them and the customers, the development of milking machines, quality assurance in general, drugs, and so on. So you end up with a special interest group (SIG) giving some preferences which eventually become rules and turn into government for that sector.
Discussion
But who enforces it? And why can't there be another milk provider that refuses to comply? SIGs only work when they have access to monopoly over violence, when they can force competition out of existence, which only happens when there is already a government that holds such power.
Sure, there can be a 3rd party milk provider which refuses to comply. But the game theory teaches us it's cheaper/more optimal for all to cooperate.
Special interest groups would want to collaborate so that their "special interests" are met, like raising prices. In a world where there is no regulations(aka an organization with a monopoly on violence) a new interest can always provide the same service cheaper(since prices were artificially inflated). There is a natural incentive to not cooperate, as Game Theory would dictate, someone WOULD take that up if there was no monopoly to violence.
This works because there is a natural incentive for ALL service provider AND CUSTOMERS to cooperate, which the SIGs were not doing.