You might want to look at CX's AsiaPass program if you're planning to visit 5 or 6 countries.

I don't think airfares from BKK to other SE Asian countries are any cheaper than the reverse. Nevertheless, hotels are much cheaper (and nicer) than any other countries in the region.

On one leg, from BKK you can fly to Phuket, then to Penang, Kuala Lumpur, Singapore then back to BKK. Another leg might be Siem Reap in Cambodia (home of the famous Angkor Wat), Saigon and Hanoi. Still another leg might be HKG, Manila and Cebu.

Enjoy!