One of the cheapest air fare would be Hong Kong. Food is so cheap plus there are shopping malls with bargain items. You can also go to Macau via Ferry ride, it will cost each person few hundred pesos only, in Macau there are some tourist attractions with no entrance fee like the ruins of St. Paul plus bargain shops again around it.
I agree with Stan. Normally, a Hong Kong trip is cheaper than any other country, plus a side trip to Macau or Shenzhen. Don't forget to take the kids to Disneyland or Ocean Park.
Japan. I love their dicipline and of course the sakura.