Most expensive thing will be the switch, the cabling is not that expensive.
For a 10g card to work you'll need a pair of SFP+ transceivers, one for the card, and another one for the other element you're connecting to (a switch, a router, another computer...) This transceiver can be chosen for copper or fiber depending on your needs, and each transceiver will be from 50 to 100$. Then you buy fiber or copper Cat6a cable.
But, if your two devices are near (less than 10 meters), you can use a Twin Axial DAC (Direct Attach Cable) : you won't need the transceivers, you can just directly connect the two devices with this cable into the SFP+ port, and it's kind of cheap, for example, 12€ a 3meter run:
> You can do physical loopback by connecting the two ports together.
this ! and this is waay better, because you can run all simulations (perf etc.) whatever on the same machine. for example, you can run client on 1 cpu-core, and server on another, and have packets looped over the physical interface.
