In that price range you should be looking for an Asus, HP, or a Dell. Prioritize storage, RAM, and screen over processor speed. You should be able to get an i3, with a 1 TB HDD, 8 GB of RAM, and a reasonable 15" screen for around the $450-$500 mark. Going lower you are probably going to be stuck with a Pentium, which isn't TOO bad... or a crap tier Celeron. You should be pretty happy with an i3 laptop.
What you might want to consider as well are refurbished or open box laptops. I managed to score an open box Asus 303Q a few years ago with an i5 and 8GB RAM, a $700 PC for like $500, while I was shopping around at Best Buy. That laptop served me well for 2 years, and I just upgraded a couple months ago.