ATM are ubiquitous, but most Korean ATMs don't accept foreign cards, only special Global ATMs do. These can be found at airports and some subway stations in major cities, as well as in many Family Mart convenience stores, so stock up before heading to the countryside. Credit card acceptance, on the other hand, is very good, and all but the very cheapest restaurants and motels will take Visa and Mastercard. (It is illegal to refuse credit cards unless it's a very small shop).

http://wikitravel.org/en/South_Korea
http://wikitravel.org/en/Seoul

Costs:
Korea is fairly expensive for an Asian country, if still notably cheaper than Japan. A frugal backpacker willing to eat, live and travel Korean-style can squeeze by on under ￦60,000 per day (~30Ls), but if you want top-class hotels and Western food even ￦200,000/day will not suffice. (~95Ls)

http://finance.yahoo.com/currency?u