Recombee is relatively affordable and has a generous free tier, but if it starts to outgrow your budget there are things that you can do to manage your costs. Recombee charges based on the number of recommendations requests that you make each month. In your Treefort app this number grows with the number of active users that you have and the number of places where you show recommendations. Treefort caches recommendation requests so that the same results are re-used for a period of time. This reduces the total number of requests sent to Recombee. There are two additional ways that you can manage costs:
Rely on non-personalized recommendations which can be cached once for multiple users.
Reduce the number of places where you show recommendations in your app.