If you're under 25, you're in for an unpleasant surprise when you check into the Oasis Cancun, a pyramid-like, all-inclusive resort on Mexico's Yucatan Peninsula: a mandatory "under 25" fee of $54. And they don't take "no" for an answer. When Ryan Plaxsun, 24, recently checked into the hotel, he was told to pony up the cash -- or leave.