I do sports, and when we have competitions, I bring my camera.
Usually my total of 80GB cards don't fall short, typical 8h at the tournament is 60-70GB. One big multi-day tournament got me 180GB in 3 days. That took a while to sort.
Why an amount per month?? When you are shooting X amount per event, you need enough GB to safely cover that. I found that a 64GB card will cover a event for me as of know.