My International Drivers Permit cost £5.50 and took about 10 minutes in a post office.
They stamped the motorcycle box and my UK License has provisional entitlement for a motorcycle.
Regarding the legality of then riding in Thailand, I presume it depends on what rules they have for learners ? I would be interested to hear about that.
I actually got the IDP for car hire & only after reading the small print on my insurance am I considering motorcycle hire.