Looks like they are router'ed, which while technically being a CNC machine is usually a order of magnitude cheaper than a CNC lathe or mill.

Yes, this is exactly how they are manufactured. I got them from Schaeffer AG [1] and the three plates cost approximately 300€.

[1] https://www.schaeffer-ag.de/

This was confusing to me as well. I have a CNC router, and I, along with most readers, would probably equate these things. For all intents and purposes, CNC === CNC router, or at the very least expensive, uncommon equipment in a home shop.

that is _really_ high. I can get those 3 water jet cut for ~$100 at a commercial shop down the street, alot less in volume

Are you including the cost of materials? (And in this case shipping)

I could cut these out on the plasma table in my garage for free, but that looks like at least 150 bucks worth of metal.

really? steel for me is $0.80/lb, and Al is around $4

Where?

I haven't bought much aluminum lately, but I used to go to Alco in San Leandro (Bay Area). Steel I get from Bay Steel, which is right next to my shop. it might be up to $.90 (?)