No one other then probably Dave D, Mcbeth and his family probably have any idea.
Frankly, I think 144k is low. Between sig series royalties, Tour Series sales (thru the roof), PDGA winnings/innova bonuses for said winnings I bet its more then that. That's also not counting any breaks or perks he might get toward his touring expenses. You think he wrapped his massive tour trailer from this year with Innova logos everywhere for FUN?
All I know for sure is that at some point last year McBeth posted here on DGCR a pretty tongue in cheek question that suggested he made over 100k in disc golf income in 2014. Its not anything for sure to go off of, but this is the thread for rampant speculation, and the way he said it made me take him at his word.