Forgot to say, personally, if you want to buy it online and don't feel like dealing with eBay just use Amazon. They always have about the best new prices you can get. Of course that's assuming you have Amazon Prime and can get free two day shipping.
Otherwise, just go to Gamestop, Walmart, Best Buy, ect.
If you want cheaper and used, search around on eBay and you can probably find a decent deal or bundle if you're lucky. Just make sure to read the description. I wouldn't really bother buying new from eBay unless you find an incredible deal, and in that case, just make sure to check their feedback.