PCI Raid Card

Your PC has a PCI slot and you can use a PCI raid card in there but you have to consider:

1. PCI is a very old standard. (From the 1990's) It only supports up to 133MB/sec transfer speeds. Which limits any modern storage device.
2. PCI raid cards are not being made new anymore. You can still find them as new old stock and secondhand. But getting drivers and support for modern Windows versions may be problematic.
3. Check if the raid card requires any additional power connections. Old cards may need old power plugs like Molex which your PSU does not have.

Considering this, I would recommend buying a PCI-Express raid card instead. Or maybe better: use the built-in Intel firmware raid. The Intel raid will give significantly faster boot times because standalone hardware raid cards usually take quite a while to initialize during BIOS boot. This system can have maximum 2x 3.5" HDD. Which can make just one Raid 1 set. Of course you can partition this to make as many disk partitions as you like, and all will be protected from a single hard drive failure by the Raid 1 technology.