Well, you can find them on some online shops and ebay... those usually list the prices in United States Dollars (USD). If you need to though, there's
xe.com, which can give you an estimate of how much USD Japanese Yen (JPY) is worth, and vice versa. It can be handy. :3
I tend to estimate just by moving the decimal point over, when it comes to yen. So... like 500 yen is a bit less than $5.00. Using xe.com, it comes out to $4.85. 2,000 yen is a bit less than $20.00... ahh $19.41.