I think a public guillotine event could raise enough money to put a dent in the national debt.
Though swimming with hungry sharks might do it, too, if there is super slow mo underwater cameras and the sharks are really small so that it requires lots of attacking bites.
Piranhas?
Maybe toss a life ring floatation device so that it's not a simple drowning!
Give a rule that says, "if you can make it to the 8 minute mark, you can be pulled ashore," without mentioning the hyenas waiting there.

Wait, this has been a successful series, no? I'm sure Okaydo can provide some Hollywood entertainment facts so we can estimate revenue if we can only get the right "personality talent" as our next guest contestant.
Actually, we could make a list of them and it would build to a crescendo, grand finale, with Marie Antoinette and King Louis XVI. We're going Back, To The Future!