I believe the idea is NOT to play multiple $100 matches. Its for all players who want in, to ship $100 to a 3rd party as an entry fee. So it costs $100 to get in (not multiple $100's).
Then you play your match with your opponent at whatever stakes you want. Tiny stakes is fine (or even play money if they have play money HU anywhere). The idea isnt to win alot of money during the matches. Its for everyone to pitch in $100 up front and the winner to win the big pot.
It could go something like
8 players....winner gets $800
9-12 players...winner gets 75%...2nd gets 25%
13-20 players.....1st 60%...2nd 30%...3rd 10%
So, again, it only cocst $100 to play...plus a max of 2 stacks (if you lose 2 matches to none) and a "stack" could be as low as whatever the lowest HU stakes are where you decide to play.
After the whole tourney is over, there could be some sort of thing like Aisthesis suggested where the champ is required to meet any challenge to his title.