According to NPR, a Congressman on a powerful House committee can raise up to an extra $250,000 in campaign funds from lobbyists because of his political power over the federal tax code or affected industries. In effect, this is the going "market rate" for his level of political influence.
To eliminate this corrupt "market", we shouldn't be trying to "limit money in politics". Instead, we should limit government, so that it can no longer interfere with a genuine free market.
Here is the opening:
What's the going market rate for a friendly Congressman?(Read the full text of "The Best Congress Money Can Buy?")
Of course, it's illegal to bribe a legislator. But according to recent episodes of the NPR shows Planet Money and This American Life, Congressmen on powerful committees have a much easier time raising money for their campaign war chests than members of less-powerful committees. And this political clout can be measured in precise dollar amounts...