Copiapoa hypogaea ?

It looks a lot like my cereus peruvianus monstrose.

No, definitely not C. peruvianus. I think Copiapoa species for sure after looking at some pics, but i'm not convinced that its Copiapoa hypogaea...though that's close enough for me and i wrote it down on a plant label and stuck it on the pot... ;D

If it helps, C. hypogaea v. barquitensis is probably the more specific name.

There is lots of variation within this species - some are brown with neat tubercles, others are green with "untidy" fuzz and protruding tubercles

I would call it Copiapoa humilis and not hypgogaea.

Hi,
That's a Copiapoa for sure, but I don't think it's a C. humilis nor C. hypogaea. It looks somewhat to C. mollicula, but it probably is still another species. Looks like some of the shoots are etiolated, so this makes it more difficult to give a poper ID.
Regards,
Pieter