There are many misconceptions of Japan regarding the cost of living. While some things are darn expensive, somethings can be dirt cheap - especially with the existence of the good ol 100 yen shop.
When I came to Japan as a visitor during my teens, I'd make a point of spending time in a 100 yen shop or "Hyaku en shoppu" (百円ショップ(ひゃくえんしょっぷ)).
I'd pick up cheap presents for the lads in the 100 yen shop and spend the rest of my hard earned dosh on games and Idol photo books in Akihabara.