By the way, I was in Japan during Christmas week too. The price was 7800yen, but I stayed there for like 3 weeks or so, it was suppose to get more pricier during the christmas holiday and the new years, but they keep my price to 7800yen per night.
Internet sucks to find deals on Hotels, I think, try one of those travel agencies in Chinatown. If you book directly from Sunshine Prince, it'll be around 12000yen to 15000yen a night. If you are in Seattle, I can recommend you a travel agency that will give you a good offer.
Just to let you know, in case you don't know this, Ikebukuro and Shinjuku is quite far. Ikebukuro is at the end of the line, and Shijuku is almost at the other end, but the whole trip won't take you more than one hour. Ginza, Tokyo, Akihabara and Ginza are between the two lines. I hope my memory is still as good, since I was there almost 3 years ago...hehe. It also takes about 1-2 hours to DIsneyLand, and I think you only need to change 2 or 3 lines.
Hmm there is this hotel just outside of Shinjuku, JAL CITY, you can walk 10-15 minutes to Shinjuku. THe hotel is nice, and the receptionist was pretty hot, she can speak good English too. I didn't have any reservation with them, I just came over and reserve a place for a few days, I think the price was below 15000yen. It probably will be a lot cheaper if you book from a travel agent.
So good luck, let me know if you need anything.