You can send them the json for their user page and a copy of your user data policies. This process can easily be automated with an url. This doesn't cost more to do than any other form of customer support.

Then store less customer data. You're complaining that being data leech is expensive because of the GDPR. That's the point.

Europeans don't want you to keep that much data on them. If your business model requires that, it is not one we want to encourage.