I think you could consider it more a limitation on how much they are permitted to spend on the media, such as commercials and the like. If all sides are treated equally I don't believe there would be any violation of first amendment rights. They can still say what they want on the stump, at meetings, at rallies, etc. They would still get news coverage, provided that coverage is equal and unbiased. Just limit their paid commercial time.
And I like the idea that all candidates are funded equally, from a public fund set up for that with voluntary donations. All donations made to a joint fund, not to a particular party. That might make it even more likely that the candidate with the best platform will be elected, not the one with the best funding.
Of course, this is all fantasy. About as likely to happen as the moon falling down. Oh, well. It's a nice dream, anyway.