I just got off the phone with a prospective customer who is shopping for replacement air conditioning equipment.  I would like to share some advice with you about buying a new air conditioner.  DO your homework before you need to buy.  There is a great web site at www.acca.org that will help you to better understand the buying process. 

Briefly, you should look at: 1) The manufacturer, because contrary to popular thought, not all equipment is the same.  2) How it is installed; will it be installed by a Tech or an installer or even worse by a subcontractor.  The life of your equipment is largely determined by how it is installed.  3) what kind of labor and parts warranty comes with it. 

If they are the lowest price, it is because of either labor or equipment cost.

Please - don't ask your neighbor - talk to a pro