Actually, I believe an individual is free to pay for whatever campaign ads he wants, without any restrictions. But he must act as an individual, not as a committee or an agent for someone else.
But you can only legally contribute $2000 per year to a candidate directly.
What's proper about that limitation? If I want to peaceably assemble with others of like mind, and we wish to spend our money in concert, who are you to stand in the way?