How much is the money really

I think the standard amount (if withholding is chosen) is 30%. So they would get about $35,000.

Not sure, but they might be able to choose to get all the 50k with no withholding...but they would still be liable for the taxes owed come April 15th.

Richard 'Whatshisname' who won one of the first 'Survival' payouts took his winnings without having any withholding taken out...but he never paid the taxes on it....and did time for it.

I have been on multiple game shows in the US (not wipeout) and my cousin won about $4000 on let's make a deal last year. She received the amount in full. However, you have to declare that money on your taxes (there's actually a special place on your tax form to declare game show or lottery winnings!) YOU are responsible for declaring and paying the taxes on your winnings. (You can try to hide the fact that you won the money of course, but we know how well that usually works out.)
Another family member won about $4500 on Wheel of Fortune in 2010. Same thing. He got the check in full but had to save money for tax time to pay the taxes on it.

Now, things may be different if you win a huge amount ($1 million, etc.) but as far as I know that's how it goes.

that's a nice amount of money for a weeks work.

I expect the show requires the winners to fill out a W9 and reports the winners as 1099 or something.

Actually, this season was only $25k for the winners of each episode, and contestants could win an extra $25k if they won the Tournament of Champions.

The payout is treated like income tax, you are issued a 1099 and are deducted at the max rate with Federal (~28%) and CA (~9%) state taxes, social security (6.2%), etc. In the end you only keep about 56%, but can get a tax refund if the "income" was overtaxed when you file.

Those who didn't win also get $10/day cash "per diem" for gas. In reality, that only covered gas from Burbank (CBS home location) to the filming site, and back.