Who pays the bills?

What I would like to know is where the money is coming from to fund the politician's campaigns. Why is no one asking to see the running records of incoming funds for each of the politicians and the party as a whole? It wouldn't have to name individual contributors, unless the contributions were over a certain amount, but certainly any corporations or unions that spend their money on campaigns should be public knowledge. The reason being that after the elections are over the ones who contributed towards their successful campaigns expect something in return. And, since the "winners" don't want to bite the hand that feeds them they must promote or make decisions that will please their benefactors. At the same time, the elected candidates must appear to be doing what their constituents wanted by electing them. Or, at the very least, making sure their constituents don't find out what they're really doing and saying in office.
I'd love to hear from past politicians about their experience in balancing this delicate balancing act between funder and voter. Any takers?
I've heard first-hand what it's like to have to tow the party line and the penalty for breaking those rules, but I've yet to hear much about the price politicians pay personally, not just financially, for any missteps they might make while trying to please their funding bodies. And, how many of them must they please in order to stay in the good books? And, if they remain a back-bencher how much less are they "worth" on the funding market, so to speak?
There must be articles or books on this subject by now. I'll start searching.
I think we need to know this so that the public is fully informed and can make their decisions based on more than personality or party lines.
Ultimately, the question becomes: Is our country corporate-led or people-led (i.e., without fear of losing their position other than through open, accountable elections)?