You don't need to pay a fee to report your 90-Day but if you don’t submit your 90-Day Report before the due date or seven days after it then there is a fine of 2,000 Thai Baht (about $65 / €60).
"Thank you Apiporn an Miss P for advising and helping me through the complete retirement visa process. They’re a friendly polite team you want to keep in your contact list to help you transition into your new Thailand life."