Tax campaign related spending at 200% after you hit a limit, and distribute the money to smaller candidates so donating more becomes self defeating.

There is no hard cap and no limit on doing things that don't cost money so no one is ever prevented from speaking (that would open censorship challenges). It doesn't need to survive strict scrutiny because all candidates are treated equally making it viewpoint neutral topic discrimination. And Congress has a long established power to tax basically anything they want.

I believe Hawaii already has, by redefining what rights corporations have under their state constitution. If every state followed suit, the problem would be solved.

There always was. You just have to make sure your Supreme Court isn't bought and paid for by the same people who wish to buy elections.

What do you want to ban?

There's a free speech issue to saying "you can't advertise your own opinions". Where is the line? Should every charity that "raises awareness" be banned? Should every sponsored Youtuber be forced out of political commentary? (I mean, I don't hate the idea completely ....)

There's the skeezy links behind organisations that support a political stance, and claim no real links to politicians. But we know that it's all kinda bs with strong links between the "nonaffiliated" "Political Action Committees" that claim to just represent causes and ideas, and the politicians who just happen to be close friends with the organisers. But it's rarely totally black and white.