The best PCIe 4.0 SSD we've tested is going cheap at Amazon UK | Rock Paper Shotgun
Amazon.com: Inland Performance 2TB SSD PCIe Gen 4.0 NVMe 4 x4 M.2 2280 TLC 3D NAND Internal Solid State Drive, R/W Speed up to 5000MB/s and 4300MB/s, 3600 TBW : Electronics
Amazon.com: Samsung Electronics 980 PRO SSD with Heatsink 1TB PCIe Gen 4 NVMe M.2 Internal Solid State Hard Drive, Heat Control, Max Speed, PS5 Compatible, MZ-V8P1T0CW : Electronics