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No dedicated hardware required. Bridges can be placed on virtual interfaces. You often see this happen with things like VMs and containers but you don't even need that specifically.

Works fine on a pi with either usb interfaces or virtual ones.

If you want to experiment at a low cost, though, there's the Banana PI BPI-R1. A ~$70 linux ARM dev board with 5 GB ethernet interfaces.

You can even bridge an interface to a tun/tap device, which is quite useful for VPNs and doing your own packet-twiddling code.

It's a linux software bridge, and should work on raspberry pi.

Yep. Just finished teaching a networking course using the pi as the basis for labs and projects. Had a scenario that required students to set up a bridge. Just plug in a couple of usb network adapters.

Bridge works very well on a RaspberryPi within the physical hardware limits.

An example using bridge to packet capture. https://github.com/williamknows/PiTap

You can also do this with a VLAN interface. At my recommendation, a friend set up Raspberry Pi at home connected to a VLAN capable switch to break that one Ethernet interface out to 7.