The bank is going to charge Tesla for a repurchase option, but if Elon makes it himself no charge to the company. If Elon really believes in his product then that option is one that will never get taken up, thus costing him nothing.
The repurchase option insures you against your reality diverging from Elon Musk's expectations.
Put it this way: Portugese Insurance Group (PIG) sells you an annuity that it promises to repurchase should the market crash. You find out PIG would go broke if it had to repurchase even 1% of outstanding annuities. "No worries," the broker assures you, "we really believe in this product. You will never have to take up the option."
