Can I pay for a reentry visa at Bangkok Airport if I have a retirement visa?

It's a reentry permit.

Cash

Yes you can they have office there

In BKK use International Departures 2 and it is after security but down the escalator before Immigration where you stamp out

You can get a re-entry permit (not a visa 🙂 ) at either Suvarnabhumi or Don Mueang before you fly out. They are open

To get re-entry permits for the "regular price" (1000baht single/3800baht multiple) You need copies of the data page of your passport, your current visa/extension, your most recent entry stamp and a passport sized photo

OR

You can pay 200baht more and just give them your passport (1200baht single/3800 baht multiple)

Tell the officer when you go to stamp out you want to buy a re-entry permit