Look for an Acer laptop with 4gb of RAM, an ATI or nVidia graphics card, and a dual core processor. It might not run it with every setting maxed, but it should at least run it on medium. Acer laptops are usually ~$100 cheaper than their competition, and I haven't had a single problem with the two that I've had for over a year. If you don't trust Acer, remember, they make gateway (and used to make packard bell) so it's not like they're just some shady Chinese company; they've been around for a long time.
:EDIT: This is pretty much the exact laptop that I was thinking of, and it's right at your price point.\
Acer Aspire AS5542G-5281 NoteBook AMD Turion II M500(2.2GHz) 15.6" 4GB Memory DDR2 667 320GB HDD 5400rpm DVD Super Multi ATI Mobility Radeon HD 4570
http://www.newegg.com/Product/Produc...82E16834115727.
It has 4GB of ram, a 320GB hard drive, an ATI 4570 dedicated graphics card (with HDMI out), and a 2.2GHz dual core AMD Turion II. My girlfriend has an older model of the same laptop with an ATI 3200 and an older model 2.2GHz dual core AMD Turion. It runs Sims 3 maxed out just fine (the only game she plays lol). I put CS:S on it the other day and it got about 60 frames with just about everything maxed. The laptop in that link would be even faster than my gf's because of the newer CPU and a much better dedicated graphics card.
I would also like to get a laptop to runs some of my games on.. If I had the money right now, this would be the laptop that I would purchase.
: DOUBLE EDIT :
I almost forgot about this deal. Very similar specs to the one above, but it's refurbished. It's only $435, so it's a great deal. It's up to you as to whether you're comfortable buying a refurbished laptop.
Asus X83VB-X2 14.1" Laptop Intel Core 2 Duo T6400 2.0GHz, 4GB, 250GB HDD, NVIDIA GeForce 9300M, Webcam, Windows Vista Home Premium 64-bit (Navy) - Refurbished
http://www.buy.com/prod/asus-x83vb-x...tml?adid=17653