Don't bother buying onboard or at the airport as you'll end up with a low quality plastic model (and pay too much). The models at the TG ticketing office aren't much better.
For a
very good quality model in the THB2,100 to THB2,500 range, here's the drill:
- Catch the train (express or regular) from the airport to Phaya Thai
- At Phaya Thai, switch to the BTS and take the Sukhumvit line to Siam
- At Sian, switch to Silom line to National Stadium
- Exit the BTS at National Stadium and enter the MBK Centre shopping mall (connected right to the station, 2 minute walk)
- Go to Toy Studio (stay on the same level when you enter MBK Centre) - this places specialises in aircraft models
- Reverse process back to airport
Toy Studio has a huge range of models... from the 1:500 diecast variety to 1:100 polymer resin models. It's these that you're after - they're the industry models you see on the desks of airline execs! I recommend a 1:140 TG 747-400 (comes boxed and it suitable for carry-on).
Allow 30 minutes to clear immigration from when your plane lands, 1 hour to get to Toy Studio, 15 minutes for shopping, 1 hour back to the airport, planning to be there 1 hour before your flight. That's 3:45 hours. Another 1 hour for contingency, and you'll need a total of 4:45 between flights to make this work.
Happy travels.