Don't buy new. Get used enterprise gear from ebay. https://www.ebay.com/itm/155513202027 is $13.50 and should work great, I have one and a half of this card. You'll need to run the silicom software once to set it up so it's never in bypass mode and you wouldn't know it wasn't a regular intel quad nic. You can get used dual 10g-base-T nics for not much more, although 10G switched are still expensive.
Edit: found a cheaper one $18 -> $13.50
Edit: found a cheaper one $18 -> $13.50
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