I've had great luck with the "dell outlet" where dell sells "scratch&dent" computers. My last 3 have been from there,they were all flawless, and are still in use today.
Dell Factory Outlet
No matter what brand/model you get, before you buy look up the service info for the particular machine. When you get it you want to replace the stock thermal grease/thermal pad on the CPU, GPU, bridge, etc. with "artic silver 5" or "ICD 7" thermal compound. That is the secret to getting long life and low temps from a computer.
From the factory, manufacturers use thermal tape that is "good enough" to last maybe 6mos->2 years, and is constantly letting the CPU get hot. Switching to one of the aformentioned compounds can drop your temps 5°F-15°F, increasing your speed, battery life, and CPU life. I have brought 4-5 laptops "back from the dead" by re-applying thermal compound
If you can handle disassembling the fine internals of a firearm, then you can easily handle a computer-just watch out for static, and make sure it's unplugged when you open it up :p