The cost of manga in Japan varies. You might find bargain bins with cheaper options, but collector's editions or limited releases can be quite costly. Also, it depends on where you buy them - big chain stores vs small indie shops.
Well, to publish manga in Japan, you have to have a unique and engaging story. Also, your art style should be appealing. Then, research different publishing houses and follow their submission guidelines carefully.
First, you need to have a well-developed manga manuscript. Then, research and find suitable publishing houses that accept submissions. Follow their submission guidelines precisely.