I've had good luck with the SolarFlare SFN6122F 10G NICs, dual port, PCIe v2.0, use about 6W of power, and deliver line rate speeds. Can be had on eBay for $35-40, so pretty cheap.
They're supported by FreeBSD, so they work with FreeNAS/TrueNAS. You have to load a vib for ESXi 6.7, but that's...