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).
"I contacted them when I realized I needed to get a 60 day visa in my own country, USA, before arriving in Thailand. They quickly responded to every email... I was very pleased with their service"