This is an actual fare for a flight from Portland, OR to Norfolk, VA. The base price is listed along with its accompanying fees and taxes.

If the most you would be willing to pay is $300, you would not pursue this fare. If it were listed as $265, however, you might. Why is this a problem? Because the airline would be able to raise the base fair to $300 and still keep you interested. But when it comes time to purchase the ticket, you would find yourself paying about $45 more than the $307 you currently would pay.