Northwest airlines is one of the cheapest to fly to Narita if you buy online way in advance but no harm trying today.
Like Shanghai, there are 2 airports in Tokyo. Depending on where you will go in Japan, sometimes it is better to fly to Haneda (Hongqiao equivalent) than Narita (Pudong equivalent) as most domestic flights takeoff from Haneda (eg. if you're planning to ski in Hokkaido) and it is quite a hassle to transfer between airports. MU, FM, JAL and ANA flies from Hongqiao to Haneda, but usually more expensive than flying to Narita (I got mine from Ctrip a couple of months back. It is quite expensive as I checked again yesterday). From Japan, however, you should be able to benefit from special domestic flight/train fare for tourists which you have to buy before arriving in Japan.
www.japan-guide.com has all the info you need to know.
www.snowjapan.com has all the info on where to go and list of accomm.
Have fun!