Not saying it's easy, but if you want raw data, there is a lot out there.

    FEC filings from the last few decades: http://www.fec.gov/data/
    Bills and legislators: http://www.govtrack.us/
    Lots of data, but hard to access: http://votesmart.org/
    A nice tool/repository for extracting and sharing data: https://scraperwiki.com/

This is just the tip of the iceberg. I'd be happy to talk with anyone else about finding what they need.