From 1971 to 1984, the WSOP Main Event was $10,050 to enter. It was $10,000 to buyin (all going to the prize pool), and $50 for the entry fee (going to the house -- in this case, Binion's Horseshoe).
Then, on May 7, 1985, a new federal requirement came into effect which forced casinos to report any cash transactions in or out in excess of $10,000. However, $10,000 exactly was still okay, and could be done without these reports submitted.
For that reason, Binion's decided that, effective that year the buyin would be $10,000 even, with $0 in entry fees taken.
Laughably, they revealed the reason for this to Poker Player newspaper. At the time, this was actually legal. In 1986, this became a federal crime known as "structuring" -- setting up cash transactions specifically to avoid having paperwork filed with the government.
The following year, the buyin was still exactly $10,000, but entry fees came out of that amount. It still exists that way today.
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