To get you in the mood, there is a NHK World Series called Tokyo Eye with the primary aim of providing information to potential tourists to Tokyo. They made an Accessible Tokyo episode a couple of years ago which should be of interest.

The thing is, they are gearing up for the Olympics and accompanying surge in tourism so that the program is now called called Tokyo Eye 2020. They'd be crazy to ignore that 2020 also relates to the Paralympics and that visitors to both events will include more people with disabilities than ever before.
In your shoes, I would actively contact the Tokyo Eye 2020program makers and see if they have come across any examples of suitable accommodation in your price range. They are due an update for their accessible Tokyo program, so your query will certainly benefit them by helping them understand what actual visitors actually want.