On harbor drive there are several hotels that are closer and they range from $75-150.
I suggests using hotels.com looking up the destination "Disney's California Adventure" this will list the harbor drive hotels first. The first page of results is usually all walkable.
Also you should look at these very informative threads.
We are also planning on going in Dec.(3rd to 10th) 2011. We will be staying at the Tropicana on Harbour it has an excellent location. We've stayed there before and really enjoyed it.
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