That's not a PCI enclosure, it's a PCIE enclosure. It would not work for an older PCI card.

Second the others’ PCI to PCIe distinctions

If what you need is indeed PCIe, most modern laptops have such an interface, it’s just shaped inconviently.

You could get an M.2 PCIe to PCIe adapter like this one: https://www.digikey.com/en/products/detail/dfrobot/FIT0782/14322643

After doing some research, it seems the modern way of approaching this is to get a Thunderbolt dock for laptops. It has to be Thunderbolt and not just standard USB-C, even though they both use the same form factor.

I found this as one of the cheapest options at $140: https://www.amazon.com/dp/B0FQ7VXYDJ

You would then get a Thunderbolt to FireWire cable, which is a simple cable and less than $10.

The problem is that FireWire is incredibly picky about power delivery and so anything that officially supports FireWire also has to have a really antiquated specific power delivery spec that no one is streamlining anymore. So it’s unfortunately niche at this point.

But a lot better than $4k!

Just to clarify, do you mean PCI (old) or pcie (new). I'm assuming you mean pcie since it's thunderbolt.

If I'm right you can get a pcie thunderbolt GPU dock on eBay for like $70 (without power supply) like this

You'll need a separate ATX PSU

PCI or PCIe? They are different, so make sure you get the right thing.

PCIe thunderbolt cards can be found on aliexpress for $70-100 AUD.

I have this one:

https://a.aliexpress.com/_mLsmPzv

You need to have a thunderbolt port (not the same thing as USB, check your device specs), and you need a power supply, I use an old PC power supply.