(Amazon or Newegg) WD BLACK SN750 500GB NVMe Internal Gaming SSD – Gen3 PCIe, M.2 2280, 3D NAND $70

This is currently one of the best performing M.2 NVMe SSDs on the market (better than Samsung EVO 970, although it depends on which benchmarks you use). The triple camel says it’s the lowest price so far. Unfortunately only the 500GB is on sale.
Review
Update: not currently in stock, ships on January 25th
Update 2: same price at Newegg , currently shows in stock