This is way too expensive for a few SMS. Can you please negotiate with AIS for a price per SMS?
And please check also the other mobile providers in Thailand (True move and DTAC), because here we would pay 100 Bht per SMS, which is too expensive.
If we cannot find another one, we will use the one from Australia, which costs 12.5 Bht per SMS even it is in Australia.
If there are any questions, please let me know.