Just to be clear, 2,000 Baht is the minimum fine.
If a foreigner staying in the kingdom over 90 days without notifying the Immigration Bureau or notifying the Immigration Bureau later than the set period, a fine of 2,000.- Baht will be collected. If a foreigner who did not make the notification of staying over 90 days is arrested, he will be fined 5,000.- Baht.
https://www.immigration.go.th/?page_id=1666