Were you stamped in for 30 days? I'm pretty sure you can go to immigration and get an extension for 1900 baht. But try early as they add the days on top of your admitted until date.
Even if there was an ATM airside, it wouldn't help a lot of people. My visa, for example, has a daily max. I'd only be able to withdraw a bit less than 10k. Then I could of course just sit and wait for 24 hours :)
I contacted them out of curiosity after seeing one of those get-a-yearlong-visa-ads on FB. After a bit of back and forth, an ED visa was all they could help me with (not being 50 or married.) They seem to know what they're doing.
Just relayed my experience. The guy was looking at my passport with a concerned expression. Then I handed that letter to him and he lit up like a christmas tree and made my account. It most certainly makes things easier.