I have linked below the cards I bought. The prices change all the time, including from purchase to recording to posting. There are also X8 cards, dual cards for nvme and sata, and a few others. Search "X4 PCIe to NVME M.2 Adapter Card" and go by low to high. There are many sponsored options but should always find something for 7.99.
The purple card can be found here:
https://www.amazon.com/1PortNVMeAd...
The black card can be found here:
https://www.amazon.com/ProfilePCIM...