I recommend using http://www.craigslist.com
to shop around for a new 360.
I bought a pro edition for only $200 ($100 off), and it still came with a two year warranty through Wal-Mart, and I believe the three year warranty through microsoft.
You can find some amazing deals as long as you look carefully, and make sure the seller gives plenty of details on the system, and you make sure to ask all the right questions.
Also the arcade price will not drop or rise in the U.S.