You might have had this experience: You price out a plane ticket in the morning and by the time you are ready to purchase it that afternoon you find that the price has gone up or down. Usually up. These days airline fares seem bounce around like stock prices. Into this mess comes Farecast.com, a website that tracks airfares like, well, stock prices. Type in your route and Farecast returns a chart of fares history for that route for the last 69 days along with the percentage chance that the price will rise, fall or stay the same.