If you can’t meet the 400,000 requirement, you can also apply for a NON O married to a Thai from the Thai Consulate in Savannakhet, Laos.
It is a consular document, not one issued by Thai Immigration, it cannot be “extended”, you can only return to the Savannakhet Consulate to apply for a new visa before its expiration, or make application for a NON O married to a Thai issued by your local office to maintain your status.
It requires exit from Thailand a max of every ninety days. You can exit and re-enter Thailand without a re-entry permit.
It is an option if you need time for seasoning of funds, want to switch later to having a full year of deposits for the monthly option, or you just want a simpler way to get a NON O married to a Thai.