You guys are a bit out there. Heck you can find a decent laptop for about $5-600 even at Best Buy. HP and even Dell have some low end laptops that will run TOR and happen to be under the $600 range. The only problem is future proofing.
The reason I would not recommend you get only the laptop that will run what you want now is the future. It may run things fine now, but in the future you will have to upgrade to a new laptop. When someone is getting a laptop I generally recommend that they go with the best they can afford. A desktop, you can upgrade a video card, or processor relatively easily. Laptops generally require a whole bunch more disassembly. And for that kind of flexibility, you would want a "Desktop Replacement" or "Portable Workstation" like a Dell M6600 or some such designed for businesses. Which is generally way over what people want to spend. So get the best you can afford.
Rate these things in order.
Acer makes some fairly decent laptops at a low price, but lack on features and reliability(not saying they aren't good, just that build quality is rather iffy at times)
"I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it." Thomas Jefferson