The best PCIe 4.0 SSD we've tested is going cheap at Amazon UK | Rock Paper Shotgun
Amazon.com: Corsair MP400 8TB M.2 NVMe PCIe x4 Gen3 SSD (Sequential Read Speeds of up to 3,480 MB/s, Write Speeds of up to 3,000 MB/s, High-Density 3D QLC NAND) Black : Electronics