I expect someone will make a site or app or service for managing this, which lets you maintain a "want to watch" list with optional priorities.
For each streaming service, the app would tell you which if the items you want are on that service, and how many total hours of content that is. You can use this to help decide which, if any, streaming services you should subscribe to for each month.
I have no idea where one would get the data for such an app, but this site [1] seems to have it, so I infer that it is possible to get it. They have a paid API, so maybe they could even be used as the data source.