2) you don't have to show 800k baht in a Thai bank to get a Non-O in Thailand or Australia. It is a requirement to have at least that much in a Thai bank for at least two (2) months when you apply for your annual retirement extension of stay.
1) Can be done within Thailand, arriving on a 60 day Tourist Visa or 30 day visa exemption. Either of which can be extended for addition 30 days at Thai immigration. During this time you should try to open a Thai bank account. Not an easy proposition because bank likes customers who already have a long term visa, a reason to arrive in Thailand with a Non-O in hand.
true, but they could have ended up with 0 baht, too. There's no official price for changing the reason for an extension. 2,000 seemed like an incredible value to me. To be clear, changing the reason for my extension didn't acrually extend my permission to stay. That was done subsequently at the appropriate time for 1,900 baht as usual. ;-)
the immigration requirement is that the principal must not be subject to market risk and that it can be withdrawn at any time with the only penalty being loss of interest. I have used the account mentioned above for 7 years in Phuket.
I did what you are trying to do, change the reason for my extension from education (Non-ED) to retirement without leaving the country. This was in Phuket and about 8 years ago. My understanding that it is up to your immigration office whether to offer this service or not. After getting the reason changed to retirement, I was asked how much I wanted to pay. At this I understood there was no official price for this service, but offered 2,000 baht anyway, which was accepted. It was much cheaper to me than having to leave the country. Which is to say you should consult with your immigration office to see if they will do this for you.