Cheap and reliable way to add SATA ports with ASUS PRIME B550M-K

[jazzmanro]

I have a home storage PC with this mainboard: https://www.asus.com/motherboards-components/motherboards/prime/prime-b550m-k/.
I filled up all the 4 SATA ports with some HDD's already. I also use one M.2 for a boot/OS SSD and the PCIEx16 for a GPU as I have a AMD Ryzen 5 5500 CPU (no GPU). By looking at the mainboard and its tech specs, it seems that I still have available 2xPCIEx1 and an M.2.

 

Now I bought other 3 18TB HDDs (+1 more in the future) that I want to connect but I fail to understand which would be the best option for my setup. I saw some cheap PCIE->SATA cards but they are PCIEx4 or so. I have thought about sharing the PCIEx16 somehow between the GPU and such a storage card. I've just found out about SATA multipliers and M.2->SATA cards.

 

What would you guys recommend as the best solution in this setup?

[trurl]