Originally Posted by Ratman

I would exchange what you need to for the first day at the airport, then go to the post office and withdraw funds from your credit card via international ATM. I've yet to be charged a fee, and the rate is the rate of the day. If you use your credit card in the main tourist areas there should be no problem, but in some smaller places they sometimes only take Japan-issued Visa and Mastercard. Some smaller restaurants and such will add about 3-5% if you use a foreign card. It's very safe here, and a cash society, so I wouldn't worry too much about carting around 50,000 yen in your wallet.