@ Just Bob - I would suggest that you get your retirement visa from a Thai Consulate in the USA before you make the move. When I got mine, they were a lot more liberal as far as what financial proof they would accept. I just sent in photocopies of my personal retirement account.
If you do it here, you will be jumping through a lot more hoops - entering Thailand on one visa, converting to retirement, bank letters confirming the money, etc.
Worry about transfering the money afterwards. If you want to tie up 25K in a Thai bank, it has to be in place 3 months before you extend your retirement visa. BTW - you will have to file an additional IRS tax form documenting money over 10K in an overseas bank.
If you choose to keep the money in the USA, Thai Immigration accepts a notarized statement from the US Consulate here - $50 fee, but you do not have to show documentation of the money.