Hierarchy of Extortion

The same bottle of mineral water, priced in different places:

Supermarket: ￥1.10
Foreign Student dorm convenience store: ￥1.50
Foreign Guests accommodation convenience store: ￥2.00

On rising prices:

My favourite brand of yoghurt at:

Supermarket (as of April): ￥7.00
Foreign Student dorm convenience store (April):￥7.50
Foreign Student dorm convenience store (May):￥8.00


I'm usually not too careful about prices, but this is...