I'm not exactly sure that I understand your question... are you looking for the cheapest flight destination or the cheapest place in which to holiday? Of the 3 places you mentioned (HK, Taiwan, Tokyo) Taiwan is probably the cheapest to stay in (HK and Japan are, overall, more expensive destinations) but - your flight cost will be based upon where you are travelling from and which airline you take. There are probably more deals available to HK, Tokyo would be next, and then Taipei (although if you are flying from a city served by China Air or Eva Air - they can have some good deals to Taiwan too).

Any other country in SE Asia is a cheaper destination than the 3 countries you mentioned (but it's probably more expensive to get there). They are all absolutely fascinating countries and it really depends upon your interests and type of vacation preferred.

Shout if I really missed your question (sorry!) - or want more specific information on specific countries in the region.

Cheers! Judy in Hong Kong