I married my Thai wife 36 years ago in the US on the K-1 visa. We didn’t change her last name. A few years later, I changed my last name to her last name.
From what I understand at Ratchaburi immigration, you need to deposit B400k for the first year of a marriage visa. Then you can switch to the B40k per month deposit to your account.
If one can’t get B400k or B800k, then that person who has little money needs to spend an extra B25k-B60k additionally every year. Without my Thai wife I could not have gotten it done on a timely basis.