Send by EMS is the best, because you will know who sign documents. This is great you get slip back so fast. I usually get it in 2-3 weeks. Registered online this time, because not enough time to send by post...
I don't think the 1M is worth to pay at age 61. You can live on Retirement extensions.
I not sure about current interest rates, but I once deposit 1M to time deposit (type which is accepted by Immigration) and get nearly 30k THB in one year. So, if you do this way you can get +600k on top of this 1M in 20 years...
In conclusion: I got my affidavit from Consulate (keeping in mind it valid for 6 months which is good) and also will bring my bank passbook with monthly FTT's and it's copy in case of any further questions.
Original visa information and extension information will be transferred free. Probably he will need to pay for reentry permit again if he had one in old passport - but I not sure about this and probably they will put new reentry stamp with the same number as old one to new passport...