Fees per block need to rise to 25 BTC to break even with the current subsidy, which is a fee of 0.025 BTC per transaction with 1000 transactions per block. This is $6 / transaction.
Good. How many bitcoiners send their funds paying $6 fees?
How many transactions will be daily if the minimum tx fee is $6? (Let us assume this number is X, I think X is much less than 100k)
What would the minimum fee if the daily tx number is X?