Buy second hand microwaves
Microwaves are some convenient ways to prepare some foods, specially if you are too lazy to cook. Most foods in Japan are microwaveable, which means having a microwave is really convenient. You can save more money for microwave by buying directly from fellow foreign students who will leave Japan soon.
If you are a foreigner, specially if you want to leave Japan, you can also sell your used microwave ovens here. Help fellow foreigners saving money by selling your used microwave by clicking +START SELLING button on the top right.