Need Help Installing A Car Dash Kit For A 1998 Ford Taurus ?!?

Im trying to get a dash kit in my ford taurus so I can use cds in m car. I checked out Bestbuy.com for the kits and they were around $125 and Im not sure if that even includes the installation fee. On ebay thou, I see one that is half the price than bestbuy . So should I purchase the kit off ebay or should I just go on bestbuy and buy it from there ??