[schnischna]

"In my case, I am willing to pay more to the local shop if everybody is doing it. If Im the only one, the benefit is lost but I personally pay the cost."

But a significant number of people should be wanting to do it - after all, the elected government wants it. So at least 30% of the people or so should want it, the ones who elected the government.

30% of people should be enough to keep some local shops afloat?

Also, I don't get the analogy of sharing travel costs. Shopping locally doesn't get cheaper if more people do it. Unless you build a huge mall, if that is what you want.