I think the first step towards change is to envision the world that you want, and find people that agree with that vision. And if you can't agree on everything, find that subset of policies and objectives that people can passionately agree on, and forget everything else. Then, get organized.
Start by going door to door; find people who care enough about the issue to help out; have in-person meetings and events and build connections; give people the tools--online and offline--to recruit participants and stage their own meetings; orient people towards a focused set of objectives, and ask them for money to help you broadcast those ideas with counter-propoganda; ask people to contribute time and money to candidates that support those objectives; always keep everything above board, to avoid being attacked; rinse and repeat. If enough people care, you can win; if not, then maybe "money in politics" wasn't the real hurdle to reform--maybe it's just that the voters didn't want the reform you were preaching.
Democracy today seems broken, like it doesn't work any more, but it's always been "broken," it's never "worked". The progressive movement and the labor movement of a century ago both fought an uphill battle against big money in politics. It took decades before they experienced lasting success. When voters want changes in government that cost profitable businesses money, a lot of those businesses will spend at least as much money as they stand to loose to prevent that change from happening. It was as true one hundred years ago as it is today.
The fact is, though, that absent massive violence or election fraud (which itself is only possible when the polls are tight) with all the money in the world you still need people--individual people--to vote your way. Money in US politics has influence only insofar as it can be used to convince the masses of voters to vote a certain way. The thing is that money and propaganda have limits, especially if a message of reform resonates. That's what social movements are all about--coalescing around a message of reform that makes propaganda sound unconvincing.