As with most things in Thailand the easiness is a variable dependent upon the location of the Amphur, the person you are speaking to, the phase of the moon, etc. However, it is not beyond most people to accomplish it. Best place to start is the website of the Embassy of your country, you will certainly have to interact with them to some degree so may as well start there. In case you are from USA, for example, try here; https://th.usembassy.gov/u-s-citizen-services/local-resources-of-u-s-citizens/getting-married-in-thailand/