Are you a student? If you buy from apple, youll get a discount. If you are going to custom build it then you have to buy from apple if not try amazon usually cheaper than apple.
I just purchased a 24in White iMac (refurb) from Apple. It was $1449 plus tax and free shipping. Pretty darn good deal for a 24 if you ask me. If they do not have any listed in the refurb section check back day to day because they come and go. Has the same warrenty as the new iMacs. Good way to get a 24 and save some big bucks!