Groceries in general are fairly cheap in UK compared to much of Europe.

I would heavily recommend just getting a router that supports OpenWRT, there's loads of choice, but for entry level I would suggest TP-Link Archer C7.

If you don't care about wifi, the Cisco Meraki MX65 has 12 ports and is very cheap right now.

Most equipment these days uses SCPI which replaced GPIB, some still use the GPIB connector, but often they just use USB serial (CDC ACM).