Multi Geo in Power BI Cost

You will just need to pay for that additional P1 capacity. Adding capacity cost money, but there is no additional cost in running multi-geo.

You can also, use your current P1 (8 cores), and set up 2 capacities each with 4 cores with different geo. So cost will remain the same, but the capacity limit is halved for each capacity.

Less core, less compute capacity, lower limit.