Limit Worker requests when on a paid plan

I am considering switching from free plan to a paid plan. All requests to my site go through a Cloudflare Worker, so I sometimes bump into the daily Worker request limit. When this happens, the worker “fails open”, so request is served from the origin.

On a paid plan the daily limit is higher (which is why I want to switch to a paid plan), but when the limit is reached, it appears Cloudflare will just charge me more and increase the limit. Since I can’t control other people on the internet making requests to my site, does this make my monthly cost unlimited?

On a paid plan, when the original allowance is exceeded, is there any way to make subsequent requests “fail open”, instead of increasing my monthly cost?

I hope I am not the first person who feels uneasy about potentially unlimited costs, and that there is a solution already.