You can pick up used HP NC523SFP or NC552SFP (better!) NICs for about $15-$25 each off eBay. The drivers fell out of support on RHEL8/CentOS8 but I think Fedora Server, RHEL7/CentOS7 and Ubuntu Server are fine with them. TrueNAS can make use of them as well. Then all you need is a 10GbE switch that can do bonding. Or, just make yourself a router with a bunch of dual port NICs.
https://www.ebay.com/itm/LOT-OF-2-593717-B21-HPE-NC523SFP-DU...