I recently posted a Registered letter containing my soon to expire UK Driving Licence, an A4 piece of paper, & a folded envelope, cost was exactly 300b.. or 95b if unregistered the girl said... Thai address on the back, plus a phone number was needed !!..this was done at one of these small sub post offices, i not sure if its cheaper going to the main post office
I tracked it, within 2 days it was at the Airport, 15 days later still at Bangkok Airport, i got in touch with" contact us" Thai Postal Services, and within 48 hours it had arrived in the uk,