Can I live in Thailand with a Non-Immigrant Type O Visa if my income is above 40,000 THB and I don't have 400,000 THB in the bank?

Choice two;

Get a 90 day single entry Non-Immigrant Type O visa from a thai consulate before you come (usually around 2000baht). Start transferring a minimum of 40K baht into the country from overseas into a thai bank account in your name only. The transfers MUST show as coming from abroad (they cannot be coded as inside the country transfers).

Go to the immigration office get the hand out that lists the required documentation, copies, photos, etc needed to apply for a year extension of stay based on marriage.

Apply for the yearly extension for 1900baht when you have 30 days or less left on that 90 day stamp you got when you entered the country on a single entry Non-O visa.

The application will go under consideration for 30 days (they usually do an in home visit during this time to make sure you're really married) then on that date you go back to the immigration office and get the year extension inked into your passport.

IF

you are going to leave the country during that year you would also need to buy a reentry permit for 1000baht for a single or 3800baht for a multiple

Choice one;

Come here on any entry you want to, go to the thai consulate in either Savannakhet Lao or Ho Chi Minh City Vietnam and apply for a year-long, multi-entry Non-Immigrant Type O <-(the O means other) based on marriage to a thai national.

Those two consulates do NOT require proof of funds to issue that visa. That visa is valid for a year from the date it's issued, it is unlimited entry for that year and you get stamped in for 90 days every entry. When your 90 days is running out, you go to the border, stamp out of thailand, stamp in&out of another country and stamp back in to thailand for a new 90 day stamp. You do this for the whole year the visa is valid for taking you to almost 15 months of stay in the country in 90 day increments

In Savannakhet that visa is 5000baht and at HCMC the visa is 200US.

The thing that causes the confusion is the blanket use of b/s terms like "marriage visa" :O

You have a few choices as far as whether you're going to go on year-long Non-Immigrant Type O VISA based on marriage from a thai consulate in another country or whether you want to get 90 day Non-Immigrant Type O visa based on marriage and then apply for a year-long extension of stay inside the country at the immigration office. They are two totally different things that people commonly call a "marriage visa" (although neither is a marriage visa :( )