Pull financial disclosures from first year they filed after entering office. Schedule III lists assets, schedule IV spread the financial statements. Too bad they're only available online for 2007 onward. Not sure how to go about getting the ones pre-2007 but it obviously involves asking the government for shit (FOIA). House FD (financial disclosure) reports and PTR (periodic transaction reports) available at link below.
http://clerk.house.gov/public_disc/financial-search.aspx
Reading Nancy's 2017 disclosure. She lists NO GIFTS. None. BULLSHIT! Durbin had something like $150k in the bank when he entered the House. Now he's worth $1.5-1.6M. I'm sure he truly earned all of his money /s. So we can't even really calculate this, accurately, since they're taking money under the table. Even if we do get financial disclosures for every member of Congress, public office holders, the before and after won't be very accurate.