At 100x the traffic the business would be at 5 million dollars a year in spend, and would exceed the standard pricing model of Heroku. The business can then

1) Negotiate with Heroku for an enterprise contract 2) Consider migrating to a more cost effective platform 3) Dedicate time home-growing a solution.

Part of the reason Heroku charges so much is because their customers are typically small, but they'd likely rather find a price that keeps you on their platform vs. home-growing a solution.