Re: You expect this from crooks, aided by lazy corporates.
"30 low-mid range PCs could easily run 150-300H/s each on the CPU alone. The ones with GPUs could run anywhere between 500 to 1000H/s."
The CPUs maybe, if they're i7 or Ryzens. Maybe an i5, none of which I'd consider mid-low range. Old xeons are about the cheapest bang to buck ratio, 150 H/s for an E52xx, 200H/s for an X55xx, running a thread per core. To get 500+ on a GPU you'll need a rx 570 or a 1060.
That's using a tuned miner run locally, not bothered benchmarking coinhive, but I'd suspect it was a tad slower.
If it's in a heated space, then it may even end up saving money, since they are remarkable efficient little heaters. If you've got a shop full of those, along with free reign to run what you like on them, then I'd expect you'd already be running some sort of mining operation.
I've suggested it to my local PC builder, but he's averse to doing anything with new (or customer returned) kit, as he then can't legally sell it "as new". While he always has a decent selection of GPUs, none of them get taken out of a box unless it's to install in a clients box. Since he's the one running a successful bricks and mortar computer retail business, I suspect he's making the right call.
"Monero has far lower requirements than the likes of Bitcoin and Litecoin, and it uses a different algorithm that doesn't run any better on ASICs than on desktop PCs."
Eh, that's not quite true. You can build an ASIC for it, but that ASIC would end up being more expensive than the equivalent CPU. Hence why no-one has bothered. You'd be better off picking up a retired HPC cluster or equivalent bulk 9-10th gen blade servers at 30-40 quid a pop.
There's at least one data centre around these parts that uses spare cycles for mining, which pays their 'leccy bill. Not worth the return on capital, but beats them sitting idle :)