"Hmm. You're going to charge me $250 a month, based on my cash balance, to keep my money in your institution. How much would it be to rent a large safety deposit box and just put my cash in there?"
Some have already closed that exit, banning the storage of cash in their boxes. They want to keep your funds available for negative interest rates and possible bail-ins.
I think the difficulty would be finding enough safe deposit boxes. If I had $100M (let me dream, will you!) where could I store that physically? That much cash takes up a lot of space.
The Oatmeal had a post where he talked about how heavy his $200,000 withdrawal was (that was in 20's).
I think Adam Curry talked about buying actual gold bullion and storing that. Still takes a lot of space and a lot of cost in storage. $100M in gold is over 80,000 oz. Two tons of gold?
Yes, you're talking about 4.7 cubic feet of gold there. Buy the island and then you'll have a place to store 1 cubic foot of gold, to pay your routine expenses.
Chase recently updated the terms on my safe deposit box to state that I'm not allowed to keep cash in there, and I doubt this was specific to me. How they intend to enforce that, I don't know.