Firestore query costs

As far as I know, if your query returns 1 document, you'll be charged 1 read. If your query returns 1000 documents, you'll be charged 1000 reads.

I'm not sure how your app might look like, I'd rather re-structure fetching process. For instance, I'd rather not fetch the entire 1000 users at once. Instead, the way of getting a fresh set of 10 or 20 group of nearby users whenever a person wants to see new users seems much better to me.

Hope this helps you.

Note: Be aware that your queries won't get any extra charges for having supplementary documents in a collection that are unread.

Have a look at Managing large result sets which help you manage queries that return a large number of results.