Castle Town Item Shop
From the Super Mario Wiki
The Castle Town Item Shop is a location in Mario & Luigi: Superstar Saga. It is found on the east side of Beanbean Castle Town and sells a variety of consumable items. Its prices vary with applied discounts, such as the one applied by the 'Stache stat. It is open as soon as Mario and Luigi enter the town (even while it is in ruins) and updates its stock as they progress through the story.