Officially 10k THB. But expect to pay slightly more at your Thai conculate. They are sometimes adding quite some premium with the money "conversion" rates.
I believe details like this will be left with the according Thai consulate at your location. Unlike with the LTR visa, the DTV does not seem to follow a centralized (pre-) approbal process. So maybe wait and see for details to be published by your consulate.
You are right. No visa does guarantee you entry. But it makes trouble less likely than on a visa exemption - espcially if you have an extensive border crossing history.