What are the costs associated with surety bonds for US money transmitter licenses?

It depends on the minimum amount as requested by each state (which varies from State to State). Grimes Law (out of Arizona) had done some work on this a few years back (it might be outdated), and the amount then was US$ 6.9 Million (at the very minimum). Applying a premium of 1.5% this would mean US$ 103,500 per year.

The financial examiner of each state can (I believe) allow a maximum of US$ 2 Million of required surety bonding for each state, if they deem your business requires additional bonding, above and beyond the minimum. If every state mandated a bonding of US$ 1 Million, you would be looking at $ 50 Million in bonding and this would mean US$ 750,000 in bonding premium per year.