Not available about PGA or USGA events. There IS a lot of money available in appearance fees, but those are only at those fake tournaments like the Skins Game and those stupid Monday night golf things on ABC. Only available, of course, to the top players--for obvious reasons.
Don't forget the "off-season" events that aren't part of the official PGA schedule. Plus, guys at the top of the world rankings (Woods, Els, Singh, etc.) can go play internationally for a big appearance fee.
THe European tour offers the big names like Woods, Daly, Els huge appearance fees. I'v eheard those fees make dwarf actual prize money. Els has not playes as much in the states this year because it would cost him too much money. A couple of years ago it was 2 mill a pop....I'llbet its more now.