Here is a simple question. I already have a retirement visa from the USA. I need to leave Thailand and come back in a few days. Do I need a reentry permit? If so, how much does it cost?

If you have an O-A visa that says "Multi" entry and the visa date has not expired you do not need a re-entry permit. But if it says "Single or 1" entry or the visa expiration date will have passed before your return you must have a re-entry permit. A re-entry permit costs 1,000 baht for a single trip.

Hold on, the OP says he has a retirement visa - I know 'from the US' but doesn't that mean he does need an exit/re-entry permit?

If you do it is 1000 baht for a single entry and just under 4,000 for a multiple annual entry.

Hold on, the OP says he has a retirement visa - I know 'from the US' but doesn't that mean he does need an exit/re-entry permit?

If you do it is 1000 baht for a single entry and just under 4,000 for a multiple annual entry.

Not if its an O-A Multiple entry..........thats the beauty of them everytime you leave and re-enter up until the 1 year validity expiry date of the visa you recieve a fresh 1 years stay stamp.

If however the OP has a standard single entry "O" and has extended said visa by 1 year within Thailand then yes he will need a re-entry permit.....as said, fee 1000 baht.....obtainable beforehand or from the office in Terminal 1 departures after check in and time permitting

The normal retirement visa (actually a non immigrant O-A) issued in the USA is multi entry and a re-entry permit is not required during the one year validity of that visa. But it is was not issued as a multi entry then the re-entry permit will be required.