Apollo has no leverage here unless there is strong evidence most of the Apollo users will leave Reddit if the app shuts down. I don't believe they will. The other potential leverage is the upcoming subreddit blackouts, or hinting at taking the Apollo users to start a competitor. The developer said they are not going to build a competitor (that was a mistake, they shouldn't have revealed that card), so I think the blackouts are the only chance of lowering API costs.