Can anyone recommend a cheap mini-pc / NUC, I only want to run Ubuntu on it.

Meerkat from System 76?

Depends what the predominant requirement is, power consumption, money, size

Why not a Raspeberry Pi? There is a Ubuntu Mate image for it.

Low consumption, cheap, small, and you get some GPIO pins to fiddle with electronics too.

It's not very powerful though.

I would prefer it to be under £100, £120 max. I know with some you have to buy ram and he’d, which I don’t mind, I have a couple of components lying around

@Fradow although I could run it on a raspberry pi, I’d prefer an X86 arch so I can avoid possible compatibility issues

If you have a spare powersupply and ssd lying about the asrock j5005 is not cheap but reasonably fast, normal x64, x265 support and super power efficient

Intel computing stick with Ubuntu pre-installed