Ask HN: Good used $300-$500 Linux laptop for road warrior?

I travel a lot for work and I already have company-issued MacBook Pro for work purposes. For various reasons (mainly to keep work stuff and personal stuff separate) I would prefer to carry a second personal laptop. The main requirements would be:

Must run Linux or FreeBSD well. Preferably Manjaro, but XUbuntu would be OK, too

Light weight. I'm lugging a ton of stuff around already and I'd prefer not having to bring a pack animal

* Compact enough to I can use it on the seatback tray in cattle class if I need to

* Decent battery life

* Expandable RAM and SSDs that can be replaced without using funky adapters would be really nice

What I don't need:

* A desktop replacement - I've got a nice collection of powerful desktops already. It does need to be powerful enough to run Emacs + C++ compiler and compiler for various JDK-based languages, but it's not a full-on development machine

Lenovo is usually my go-to when it comes to PC laptops, so I've been looking at 1st & 2nd gen X1 Carbons (fail on the expandable RAM and the SSD with no funky adapter, great otherwise) and X220/240/260s. I guess I should also at older Dell XPS 13s, but are there other laptops I should also look at?