I also like window ac units instead of central air conditioning. They are easy to replace. Also, I go to Home Depot, Lowe’s, Sears, etc… at the end of the summer season and get the manager to sell me the display units at a huge discount. Also, they have returned ac units the people bring back after using for only a few days. Sometimes people buy units that are too small for their home. When they are returned you can purchase them for half the cost.
If the ac unit is going to be put in a window it is a good idea to have the maintenance staff leave it on the floor below the window until the home is sold. Then you can avoid any issues with theft. Remember out of sight= out of mind= no theft.