Some stores sell on Instacart for the exact price they sell for in-store. Fred Meyer / Kroger, for example.

Instacart has a notice at the top of each store's page that gives each store's pricing policy. For Costco, it says "Costco sets the price of items on the Instacart marketplace. Prices are higher than your local warehouse. Costco members also do not earn 2% executive reward on Instacart.". For Fred Meyer and several others, it says "Everyday store prices" and links to a policy stating that the prices are the same as in the store.