coolgc
Pretty expensive if you don't have duct work already. Window units may be cheaper if the house is small enough and well isolated.

Overnight
One story or two? How many square feet? I wouldnt expect less than 4000-5000 USD. Central is more efficient and the cooling is more equalized but you have to get over that initial cost. If you just have a 700 sq ft house, window units can be a viable option.

GeeBeeDubyah
Good window units are fairly efficient, and much cheaper than the installation of ducting, especially in an existing home. If you live in a dry climate, look into evaporative (swamp) coolers - they are very cheap to operate, but will only work well if the outside is low humidity.

Thinker
Bri, getting free estimates from local AC/central air contractors is the key to your success in this home improvement project of yours, as the local going rate greatly varies by location. Here's a link to a handyman site that offers free very resourceful information to assist you in your project, and, ultimately, select a local AC contractor in an effort to have you get treated fairly by the contractor: INFO on AC contractors: I'm sure you'll find the information you need, specifically the tips, useful as it relates to being treated fairly by contractors and exploring the consumer-wise approach of getting free written estimates to find the best contractor in your area. . Source(s): The Internet. Just whatever is available online and what I have on my mind, including relevant sites like the one cited above that came about from my creative efforts, which is intended to be useful.