I think everyone knows that the old "Ethernet" "thicknet" is just
foam RG8U with very good shielding. I was fishing some power
BX cable in the walls/ceilings of the house, and took the opportunity
to also fish some coax for the ham shack upstairs. I figured that
I would use the Ethernet cable I had laying around as it is 50 ohm
coax. And lower loss than RG58. Not that it much matters for
HF for a 20 foot length. But if I wanted to operate 6m or 2m
it would begin to. I have a vertical in the back yard fed by about
15 feet of some rather ancient RG58 that then passes thru a hole
in the house's wall about 2 feet above grade (well sealed with caulking).
And in the basement a few feet in it meets the ethernet I just ran.
This reduced the clutter of coax inside the shack for better spouse
acceptance factor... Used a wall plate intended for phone jacks and
F connectors to make a neat termination for the Ethernet (a BNC
connector). Or if you have one an N barrel.

I don't think any IT guys use Ethernet cable anymore, so maybe
you can ask them to save some for you when they gut the ceilings,
etc at work.