This depends on the corridor and the margins on the corridor.
Typically, a PLH (Principal License Holder) will be raking in about 20–25 basis points, and would a minimum. So for every $1 Million processed, the PLH takes about $ 2,000 in income.
Anything above and beyond is the pricing set by the ISO (typically between 40–100 basis points on average and for some corridors as high as 200–300 basis points).
Ideally, you want to be processing over $5 Million per month to make it worthwhile for you.
It is never a flat fee.