Where to buy cheap, large suitcase in Tokyo

We're heading to Japan this summer using ZipAir and would like to travel light, both to save on checked luggage fee and so we don't have to move around city-to-city with a big suitcase. However, at the end of the trip we plan of buying a fair amount of souvenirs to bring back.

We could take an empty suitcase with us and use a storage service most of the trip, but I'm thinking it might be easier and cheaper if we just buy a cheap, large suitcase towards the end of the trip and only pay checked luggage fee one way.

Anyone have advice on buying an inexpensive suitcase in the Tokyo area?