A monopoly can't exist without a consumer to buy their product. They need to have enough consumers to pay them, or else they aren't going to make any money...that is the limit on the prices they can set for their goods.
If a bread congolomorate/monopoly existed and charged $1,000 per loaf, not only would most people starve, but most people wouldn't be able to pay that congolomorate and they wouldn't be able to keep selling bread at that price...it would have to go down. Don't get me wrong, I believe in some government regulation especially considering necessary goods like bread but for the most part the market will determine the price.
The beauty of a free market is that consumers and producers and dependent on eachother for their existence. A producer can't price goods too high or else they won't have a market to sell their goods in. If a producer prices too high, another one can come along with a lower price and take away from the other producer's market.