Yes, it will be ONE MILLION DOLLARS!
No, seriously, there's not going to be any charges.
Depending on how the hotspot was connected, it may not have fully registered what was going on and let you tether inadvertently. You'll be fine.
The only possible charges that can happen that you're not forewarned about is any per-minute international calling.
It was pretty cool that I was able to continue watching the WWII in color and HD documentary and my Sling TV while outside the U.S. Thanks for your response. I did call 611 and told me I should be fine and that if the hotspot was not allowed, it would be blocked. There's definitely a glitch allowing to use data on device while in Mexico thinking that you're in the U.S. (hope never gets fixed )