The Main Store in Supai is in the center of the village. Located near the Cafe, Post Office, Landing Pad, and school.
There is another little drink and snack business on the south edge of the village near the rodeo grounds. Sinyella Store.
The Main Store
We always joke there must be the locals price and the tourist price. Prices will be higher than you are used to.
Knowing the merchandise is shipped down via pack animal or or helicopter might help put things in perspective. It is understandable the prices will be higher than you are used to paying. It is not unreasonably higher. Expect prices you might pay at t gas station convenience store.
There is a pretty good variety to choose from. Mostly in smaller packages similar to a convenience store. Frozen Gatorade is my favorite treat. They have canned goods, boxed food, and limited fruit and produce. Depending on your eating choices, you actually could outfit yourself from this point if you didn’t want to backpack the weight down from your vehicle.
For those staying at the Lodge some of this really might make more sense.
I normally buy a couple gallons of distilled water and replenish my drinking supply at this point.