One of the remaining 3rd party Reddit apps (Relay) has begun discussing what it would be charging for subscription fees. Imo, they actually seem somewhat reasonable. The weird thing is that every upvote or downvote is an API call so you can rack up a huge number of API calls from voting.
Also, while the costs might be reasonable now, there's nothing preventing Reddit from jacking up prices again.
Edit: Also, there wouldn't be any NSFW content with the app.
How are you going to figure out when all you have to go on is speculation? We don’t know how many API calls Relay has in comparison with e.g. Apollo, and even if we did, wouldn’t a better app have more API calls anyway because it’s more fun to use and therefore being used longer and more often? I could make a Reddit app with very low API call numbers because I’d make it so bad that people close it after a minute ;-)