If you have a Thai bank account the amount and charges vary according to the bank. I have a Kbank account. 30,000 baht is the limit for a single card less withdrawal (using my mobile phone) there is no charge and I can withdraw multiple times.
if you already have the 12 months extension then you can renew it elsewhere. I got my first one in Pattaya and renewed in Chumphon with an updated TM30