I agree with IMOA. If you like cars and the Japan tuner scene and aesthetics, Tokyo Auto Salon should be one of your highlights. 2014 show date and place are not set yet, but it should take place on the second weekend of January at Makuhari Messe.

I usually stay at a business hotel. A single room is between 7000 to 9000 yen a night. If you want something cheaper, there are minshuku and hostels. At the very bottom there are internet cafes. I've stayed at a couple for about 1500 yen a night (1000 yen for 8 hours and 500 yen for shower).

Certain neighborhoods like Ueno and Ikebukuro have less expensive lodging.