I would take unused potential over realized bottleneck any day.
Consider that, at least in the US, local internet monopolies typically offer far less for far more.
You can, especially in the used market. I got one for $12 and a dual port one for $30. An Aquantia thunderbolt external one is ~$250, and a PCIe card is $99.
You can get Mellanox ConnectX-2 on Ebay from 12USD, these are excellent enterprise NIC's. They also consume little power as they use around 5 watt.