The rules would be simple. Set a qualifying standard, don't allow private contributions and give all qualifiers the same amount. Where's the room for corruption on the order of what we see with the present system? People will always try to finagle, but with this system the funding source would be out in the open and any additional funds collected from private sources would be hard to use, if all money used has to be reported.
And who sets the "qualifying standard"? You're just assuming that will be a simple call with no political shenanigans? Dream on...
Further, let's say hell freezes over and you manage to set up such a system with our current government (again, it's a hypothetical, let's assume it's possible). You've got a scheme that controls how much money candidates can spend. Assuming they don't find easy ways around these limits (again, hypothetical) will that really control the influence of money on the election? Will that prevent influential political pundits from endorsing candidates? Will it stop wealthy interests from lobbying for their favorite causes in a public forum? Will it stop the Limbaughs and the Maddows from "spinning" things? Or will it simply make them even more powerful since candidates can no longer spend as much money on ads?