here's my suggestion;-

Wife to Immigration Officer

Wife: "My husband has work visa but wants to give up work and get marriage visa"

IO: "We cannot change work visa or the extension to marriage extension, your husband must go to a consulate outside of Thailand and obtain a non 'O' visa which can later be issued 12 months extension to stay based on marriage."

Wife "Is there a cheaper or easier way to do this?"

IO: "Yes cancel work visa and just leave Thailand and return with a visa exempt (tourist visa) and we can convert that here to a non 'O' which can later be issued with 12 months extension based on marriage."

Wife to husband

Wife: "You need to cancel work visa and leave Thailand and return with tourist visa which they can convert to marriage visa here at this office - will take 2 weeks"

I doubt the wife fully understood all the instructions, as most of us didn't when we first came to LOS, so she opted for the easy answer - which is basically true but not necessarily the best advice.

You could just do a border hop after canceling your current extension based upon working to get a visa exempt entry (not a tourist visa) and then go to immigration in Bangkok within 15 days of your entry to convert to a non immigrant visa. You will need all the documents and financial proof needed for an extension of stay based upon marriage, After the application is done you will need to return to immigration in 15 days to get the visa and 90 day entry stamps.

Then after about 45 days you could apply for the extension of stay based upon marriage.