The vendor has the right to establish a price. The customer has the right to pay the price, negotiate a new price together with the vendor, or take his or her business elsewhere.

The customer does not have the right to unilaterally establish the price.

The price has nothing to do with the cost to the vendor. The vendor may choose to sell at a loss or at a huge markup.

If you think that Delta should accept the lower fare to CVG (the same as the SLC-BOS fare), you should call them and ask them. What do you think the answer will be?