Yes. PROs are private enterprises and charge for their services to producers.
Each commercial contract a producer enters with a PRO will have its own set of terms and conditions. It is up to the PRO and producer to determine the terms of their contractual agreement, including fees and payment schedule.
RPRA does not set the terms of the contractual arrangements between PROs and producers.
Here are the lists of registered PROs:
Hazardous and Special Products PROs
These lists will continue to be updated as new PROs register with RPRA.