Thanks to all who replied.
I called the Rio (702) 777-7777 and learned of a WSOP number (702) 777-6777, but when I called that I just got a machine saying to leave my name, phone number, and Total Rewards number with my question. So I did all that a week ago and (predictably) got no response.
So I drove up. Here's the scoop: there are satellites running all the time at the Rio with the following entry fees:
$1030,
$525,
$275,
$175, and
$125.
The $1030 one usually runs for about two hours, according to the dealers and players that I spoke to. If you come in second place, you get nothing. As one of those began, I saw players chipping in $100 each as a consolation prize. (Not sure how they planned to divvy it up. Maybe second-place gets the whole wad.) The winner gets $10,000 in "lammers."
Come July there will be "mega-satellites" in which several players at a time will win a main-event entry instead of just one.