I have a first gen X1 carbon that I recently purchased on ebay for a little less than $200 and I haven't ran into any hiccups with general usage on W10. The keyboard is really nice, but I don't think as nice as the keyboard on the x200/220, but better than the x230 from when I remember using one.

If you have $200 to spend I think the 1st gen x1 is easily the best ultraportable for the buck.