I would say you could get away with a budget of £200 per week.
Meal £2, Beer 80p room or beach hut for two £15.
I have been to Thailand, Vietnam, Singapore, Malaysia, Cambodia, Sumatra, China and Hong Kong.
I think Thailand is the most fun and mosty amazing was Lake Toba in Sumatra, you can take a ferry across fom Penang in Malaysia.
http://en.wikipedia.org/wiki/Lake_Toba