I bought my laptop about a year ago, 60 euros off some guy from a craigslist like website. It's the HP 6730b and it now runs Ubuntu 17.10. Not the fastest, but definitely worth the money.
One thing I would warn you about is old laptop batteries. Calculate an extra 25 to 40 eur/usd for a new battery as they tend to either work very poorly or not at all on those older used machines. If you know how to solder it's also pretty easy to replace the cells yourself on most models.
Would however not recommend a chromebook. Used one myself but ChromeOS is terrible even for editing documents. An older laptop with a new battery and Linux install will definitely beat a chromebook, except for battery life.