I agree with other who have suggested a $350-$400 laptop. I've always had great luck just watching Office Depot and Staples. Look for a HP or Toshiba in your price range. If you are patient you will find a machine that was selling for $600-$700 for $400. My buddy picked up an awesome 17" HP that was just loaded for $450 a few weeks back. Very nice machine. I've had a few HP DV series laptops now (currently use a DV6) and they have been rock solid. My son is still using the one I originally bought 6 years ago, and drags it back and forth to school (love the BYOT policy his school has!).
This is the one my buddy bought:
$450 after rebate but it's well worth the extra $50 will the upgraded memory, hard drive, and processor you get over the usual offerings around $400. Also has built-in bluetooth, which I think is a must for a laptop (no dongles for things like mice and easy file transfer from your phone or tablet). The screen is also beautiful on it.
The 17" screen works well for a desktop replacement, which sounds like what you are looking for.