Typically, there are three classes of service, First, Business and Coach or Economy class and seats on any airplane is assigned according to the class of service. As there are many types of planes and each airline have to figure out their own seat configuration, which often vary from airlines to airlines depending on routes, load factors and other considerations.
Now to get cheap air line tickets, one may come across when flying that the person sitting next to you have either paid less or more than the price you paid. There are no fixed prices for any class of services. It all depends upon seat availability in that class of service plus the timings - the time one passengers actually bought his or her ticket.
Also in each class of service especially in Coach or Economy class, there are often three tiers of fares, from low to high. If the lowest airfares are sold out, the left over seats are only available at higher the price and if very few or minimal seats are left, airlines have right to sell at much higher prices. Passengers buying airline tickets at last minute may end up paying more money on air tickets in this scenario. However, there is no sure way to know what will happen in the future, or whether an air carrier will unexpectedly issue a last-minute sale to try to fill a plane.
Tracking down elusive cheap air line tickets can become overwhelming, very hard, time-sucker and a frustrating folly. Cheap airfares change constantly and dramatically just when you think you have finally found that perfect right airfare. Online, the cyberspace captures it with a variety of politically correct excuses like specials cheap flights no longer available, seats oversold, black out dates etc and you may have to begin the search all over again.