Or use Agoda, Trivago, Hotels.com, Booking.com, Expedia, HotelsCombined or other hotel search service provider to seek suitable hotels in terms of budget, quality and distance from the hotel to Waseda University.
There is a hotel called 'Rihga Royal Hotel Tokyo' next to Waseda university, but it is very expensive. Takadanobaba station is the closest station to Waseda University (20 mins to walk) where there are some hotels near to.
However, Shinjuku station, which takes 20 mins to campus by subway, is one of the most popular places in Tokyo, so there is a lot of hotels near to Shinjuku.
Please click here. You can find some hotels.