Need more info. You might be able to get away with attic or crawlspace ductwork/installation if you have a single level (ranch) house. Electric will need to be run, drainage for condensate, supply and return ducts and plenum, plus the inside (air handler) and outside (condenser) units. Depending on your location, house size and installation complexity, probably a minimum of $6000 for a small, uncomplicated installation. Above that and the sky's the limit.

The house is a split-level around 1400 sq ft. I was wondering how expensive these installations are?
I didn't know electric had to be run as well.

magnolias,

Your question is similar to asking how much would it cost to buy a new car or truck?

You need to provide some details.

Read some of the threads here with folks asking for comments/advice on possible systems. There are some VERY knowledgeable people here that are eager to help you - pay them the courtesy of reading some of these other threads.

Best of luck.