There would need to be a mechanism which prevents insincere candidates from looting the common campaign financing pool. As you pointed out, the challenge is to

There would need to be a mechanism which prevents insincere candidates from looting the common campaign financing pool. As you pointed out, the challenge is to find the least bad one. In this country, many health plans require a co-pay of $10-$20 in order to see a doctor. The purpose of the co-pay is to deter would-be patients from flooding doctors with trivial inquiries who would then be able to bill insurers for their (wasted) time. So, yes, a co-pay is a disincentive, but arguably less so than the disincentives present in the system it's proposed to replace.