Am really grateful to @DrJack54 and @Liquorice for advice. I think my best plan is to leave Thailand before my permission to stay ends on 1st May. By then my visa will have expired (21 April). If I put the 400,000 into my account now I can go to a neighboring country and apply for a non o visa, married to a Thai. If I leave Thailand for Australia on 21 May I can get a reentry permit and then return in time to apply for the 1 year permission to stay. By the time I return my 400,000 will be seasoned and I should be in the required last 30 days of the 90 days of the visa and able to apply for the 1 year extension. After the consideration period my 400,000 will be free to use. I think this is the easiest way without having my money tied up too long.
I was hoping just 1 last question. Which neighboring embassy do you think is the friendliest to apply for a non o - Kuala Lumpur, HCMC, Hanoi, Vientiane, Savannakhet or any other suggestions? I did look through the forum but couldn't find much about this. Thanks.