One of the cheapest options we have seen this year for Xmas dinner in Tokyo is at the Dubliners in Shibuya but I'm sure other locations offer similar deals.
What:
Appetizer
Soup
Stuffed roast turkey
Colcannon and side vegetables
Where: the Dunliners
When: Dec 24th and 25th
Price ¥2,800/ person
Phone: 03-5459-1736
NB: Reservations are required
Minimum 2 diners required for reservation
2 hours only