Most guys I know who have played in the pro-am got the fee paid by their company. I have not seen anyone pay the full freight on their own. In all cases the company they worked for was a sponsor of the event.
@Golfingdad you need to find a new job, a big corporate gig who sponsors the Northern Trust at Riviera. Maybe even try to get a job at Northern Trust, they probably get 10-12 spots in the pro-am, you can twist your bosses arm to give you one of the spots.