yes, there aren't any ATM's before immigration, that's why I said it would solve the issue of not having 20,000 baht, but that's not the real reason they want to deny entry .
Yes, about AUD 1,000. Not a great amount for a holiday. I know some don't like to carry a lot of cash on them, so maybe access to an ATM would work, but as you said, it's usually just a simple excuse to deny entry.
With these types of comments it helps to say what immigration office you're dealing with as it is said very often that they do not all say the same thing..