Let the voting public, properly informed, consider the nature and source of these contributions in casting their votes. The biggest single reason that campaigns have come to cost so much is that television ads cost a lot of money. Broadcast television enjoys a public franchise, the frequency band they are allocated, in exchange for operation in the public interest. It is reasonable to require broadcast television to provide time free to campaigns. Simultaneously, the importance of political contributions to candidates would be reduced and political discourse encouraged.
Freedom is often messy.
One of the burdens of liberty is the willingness to allow others to express themselves even if we do not find that expression savory. The squirrels will get their bird seed, but at least the process will be open.