A second hand Lenovo is what you seek. X or T series, I'd recommend staying in the 220 series or earlier, if you really want cheap. They are indestructible as laptops, have great keyboards, decent specs and good Linux support out of the box (depending on distro, of course).
Probably should note that Red Hat outfits all staffers with a Thinkpad T series (current gen), and just did a massive refresh of a few thousands of them. T series should "just work" with no fuss. In my experience, T series has always been "no fuss". Can't go wrong with this one.
I have a T420s that was bought new and I love it as a computer -- but when I go to grab a laptop to work on 'on-the-road' I nearly always grab my old X201s + big battery that I bought on ebay for 80 bucks total.
If I was to buy a T420 now-a-days i'd check out eBay. Great deals on older hardware, especially if you don't mind repairing small problems yourself.
Yeah, I was tempted to pull the trigger on that. I recently acquired a Dell Precision M4400 for a good deal and put an SSD in it, so I'm using that with Xubuntu as my primary now.
