Apparently this research finds that consumer prices are higher (2 - 5%) in poor neighborhoods compared to wealthy neighborhoods. The inability of the poor to shop for consumer goods that are less expensive is determined by their lack of access to cars. They are stuck paying higher prices.

The benefits of a competitive market are disproportionately denied to the poor.

Doesn't surprise me at all, just based on observation. Here in Oakland, some neighborhoods get charged a steep "ghetto tax" and others don't. Add the difficulty of finding a grocery store in most lower-income neighborhoods and it gets even harder to scrape by.