What is the average cost of installation of a Goodman AC split heat pump 2.5 tons thirteen seer?

Cost may vary depends on the house size, accessibility, the amount of work involved in duct reworking, disconnecting/connecting gas electricity.

Normally, it's better to replace AC/coil/Furnace all together, since a new furnace may not be compatible with old indoor blower /evaporator coil.

Another fact is if you want have a very high efficiency and expensive 18 SEER high-end quite ac, or just 13 SEER get job done low-end AC.

It also depends on accessories (media filter , humidifier) you like to have.

Trying following links for helpful information

http://ths.gardenweb.com/forums/hvac/

http://www.hvac-cost.com

http://www.costhelper.com/cost/home-garden/central-air-conditioning.html