How much cheaper is a evaporative air cooler vs. central air conditioning?

When evaluating the costs of any heating or cooling system, consider these two separate factors: 
1.the initial purchase price 
2.installation cost

An evaporative air cooler is often touted as a less expensive alternative to central air conditioning. Weigh the pros and cons of each to determine which is truly the better bargain and most effective system for your home.

Window-mounted evaporative air coolers
Evaporative air coolers for residential use are usually small, window-mounted appliances -- sometimes called "window units" -- that can be installed one to a room. 

Roofed evaporative air coolers

Energy costs

A key consideration when weighing the costs of central air against individual evaporative units is the energy usage involved in operating each.