Is there a way to charge registered users who publish a node in a Drupal 8 site?
If I'm not wrong, the pricing process should be easier as Web services are now part of the core in Drupal 8.
Pricing should be through Paypal.
If one of the pre-existing solutions covers your use case well, you could help port it to D8 (Commerce 2.x is likely to have a stable release this year). Otherwise, you're looking at some sort of custom solution involving involving modifying the node form workflow and PayPal integration.