Is a good digital camera cheaper in tokyo's narita international airport shops or here online in the states?

In general japan will not have cameras for much less than you can find them for on-line. One drawback of buying overseas is that the warranties will not be valid in the US. They are refered to as gray market items when sold in the US. If you see a great deal on a camera from an online seller based in New York, it is most likely a gray market camera.

I actually see loads of Japanese tourists walking around in Manhattan (NYC) purchasing cameras here in the states because they can be purchased cheaper here than back at home.