I'm pretty sure anyone (except amateurs) who makes the cut gets a check, though the amounts gradually decrease as you get down the leaderboard. The real money comes from endorsements and appearance fees, though.
You'll notice that on a multiple tie in any position, the dollar amount is the same - I'm assuming that particular portion gets split among them; so in theory the guy who finished one shot worse could make significantly more money.
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.
Everyone who makes the cut gets a paycheck, with dead last probably getting $10K to $20K in a biggie like the PGA. Lesser tournaments pay off less but even a player who consistently finishes in the Top 20 will make a lot of money for the year. Results from today:
Mickelson 1ST $1.17M
Elkington / Bjorn Tied for 2ND $572K Each
Hal Sutton Dead Last $11.6K