It will not be financially difficult for Obama to cut off PAC and Lobbyist financing. However, it will be very hard on his campaign in other ways. Washington Politicians, Lobbyists, and PACs have a vested interest in keeping the current system of "Pay to Play" in place. Their very livelihoods depend on it.
I believe Washington will stop at nothing to bring Obama down for having the audacity to propose that "regular people" in America will take precedence over entrenched Washington insiders.