You want to cruise these sites:
http://www.fatwallet.com/forums/hot-deals/laptop/
http://www.slickdeals.net/
You should be able to get a dual core regular sized laptop for 300-350. Better laptops like lenovo would cost more, in the 550 range. Buying one you can modify might be a good way to get a draft N wireless card, which combined with an N router should give you more range than the b/g hardware.
I'd also advise against the small netbooks unless you have actually tried one and understand/can live with their size limitations. I have one (lenovo S10) that I really like, but they're not for everyone.