That's a really low budget for a laptop these days. You may be able to find a refurbished older model on amazon, tiger direct, newegg, or ebay, but refurb. models can been hit and miss. Generally though you'll want to look for something with at least 4-6GB of ram.
Get as much power as you can for the price. I have a 4 years old Acer, my sis has a 3 years old Toshiba, and they are both in good condition. Get new if you can, you can get 4GB of RAM and a 15,6'' screen. If you plan to carry it everyday, it's probably the biggest screen size that can be transported without too much hassle.