Food in Bermuda is slightly more expensive than in the states. Yes, some items are ridiculously overpriced, but there is usually a cheaper alternative right next to it.
For example, Arnold's Oatmeal Bread costs $8.95 for a loaf. Right next to it is a house brand loaf that is twice as big and only $5.
So, if you insist on buying your favorite name brand foods, expect to pay through the nose. If you are willing to buy local brands, the prices are still manageable.
To help alleviate the pain of provisioning in Bermuda, shop at Somer's Supermarket in St. George's on the northern end of the island. It's a short two block walk from the dinghy dock and very cruiser friendly.
If you tell them you are on a yacht, they will give you a 5% discount on the total bill. Also, for a $10 deposit, they will let you take a grocery cart down the street to the dinghy dock, making it much easier to get all you food back to your boat. When you bring the cart back, they give you back your $10 bill.
Bermuda is such a gorgeous place to visit, and if you can avoid buying fuel there, you will find the cost of cruising there to be comparable to cruising on the East Coast of the United States.