I recommend going to Thailand. With a US passport, you get a free 30 day visa on arrival. Cost of living and getting around in Bangkok is cheap, especially compared to Seoul. Definitely a great place to go shopping- pack light, bring empty luggage, or buy it there! It's approximately a 5 hr flight if you can get it non-stop. Lots to see and do in Bangkok, and several cool places to go as well that aren't too far.