I've got an 8 year old Dell Inspiron laptop that I use as a test computer for checking out other Linux distros, and it hasn't refused any current versions, light or heavy. It can't handle anything like rendering video and screen recording, but that's to be expected due to its age. So, I think anything you buy will work just fine.
I agree with minitrucker, watch the local cassified ads for someone selling. You know somebody will think they have to have a new iPad, so they're going to sell what they have to get the extra bucks. I'm actually writing this on a 10 month old Asus EEE I got CHEAP on Craigslist from someone who could not live another day without an iPad.
I wiped the drive and installed LM 10 main. It runs great!