Although it is possible to find some items cheaper in other stores, we shop there for the possibility of getting items in bulk packaging/pricing.
With the quantities that we go through, we need to buy gallon containers and 5 gallon containers of various products.
For instance, for the price of 5 or 6 tiny 10 ounce ketchup dispensers in Sosua, you could get a gallon at PriceSmart for the same price.
Then there are imported food products, simply not available elsewhere.
When I spend $1,000 US at PriceSmart, I have probably saved $400 to $500 as compared to the North coast supermarkets.
This may not apply to things like TV's, computers, pens and other sundries, but when it comes to food supplies in bulk, it is definitely worth the trip.