Welcome to the community!
It will cost $12/day for the Fido Roam in the US for the first 20 calendar days per cycle then the remaining days in that same cycle will be free and then it will reset and do the same thing in the next cycle.
You can also opt-out of the Fido Roam and go on a pay-per-use but that can also add up fast depending on your usage and if you want to go that route you will need to contact customer service to opt-out of the Fido Roam.
You can also consider getting a pre-paid line with one of the carriers over there as a cheaper alternative.
You can get more information regarding Fido Roam here.