OWC has their Thunderblt 3 10G Ethernet adapter on sale for $125.76
https://eshop.macsales.com/item/OWC/TB3ADP10GBE/
By my eye, this looks like a rebadged Sonnet SOLO10G-TB3
https://eshop.macsales.com/item/OWC/TB3ADP10GBE/
By my eye, this looks like a rebadged Sonnet SOLO10G-TB3