Sadly, the truth is that with lack of education and refined propaganda machinery it is not hard to buy vote with money. The problem with democracy is that it puts power in the hands of people, which have little chance to wield it in coordination. An informed vote is hard, almost impossible, since the complexity of society and politics is huge, the number of players huge and any individual's time to catch up and remember history very limited.
And that, without even going into the fact that there is an entire machinery to define the candidates before you get to use the vote you value so much.
So the odds are not in your favor, my friend. That said, I agree that stoping to exercise whatever power you yield, no matter how small, is to give up all power entirely. So keep voting, and, IMHO, vote for the bottom-feeders and shake the status-quo. Even a non-winning candidate that does well can gather publicity and influence that then has a chance to grow over time.