I've bought from this seller before: Intel 400GB 2 5" DC P3600 PCIe 3 0 MLC SSD SSDPE2ME400G4I | eBay is at $560 now but I wouldn't be surprised if you could get it for $500. Maybe for people like @Chuntzu in that NVMe thread this is a good one. Not much more than the 750 but better endurance.