If you are close to a consulate or embassy in your home country get the 6 month visa. It's $60 US. A single border bounce from Chiang mai will be more than that. With a 60 day you are looking at 3 border bounces depending on timing.
You are looking at nearly 6 months of travel. Better option would be the 6 month multi entry tourist visa (METV). No border bounce, fee for extensions, worry about documentation etc. Just easier.
Or easier I understand immigration is accepting payment documentation into foreign accounts. Just print out your account information. If you get monthly deposits that should be sufficient.
Sorry. Consulate or embassy takes 10 days to 2 weeks. My experience was 8 days. Your result may vary. If you use Thai mail express and US express return ($32) express you are adding 10 days on return.
If you give it to the consulate they put it in the diplomatic pouch which goes daily. Express mail will add 10 days to the delivery time. All express mail languishes in Bangkok customs for 10 days minimum.
the 800k tbh must be in a THAI bank. There is a Bangkok Bank branch in New York. This gives you a THAI bank and keeps your money in the US and in $ so you aren't subject to currency fluctuations.