It looks to me like there may be an issue with either the application of points when making the create_member call, or in the documentation of the call’s pricing.
The table at PurpleAir Develop states that adding a member to a group should cost 1 point per call, and 0 points per row returned. In my testing, each call costs 155 points per request.
I imagine this is because the call returns the sensor’s latest data (all fields) along with its success response. I’d prefer to create the groups and fetch new data separately, but in any case it should be possible to limit the fields returned.