AskHN: Cheap Home SDN Hardware

I was fortunate enough to work on a project setting up an SDN network from scratch a few years ago, and I want to carry on learning it. Since then, I've been trying unsuccessfully to find a source of SDN hardware that is priced at the casual home user. Given that you'd need a few switches to properly explore it, think £/$hundreds each, rather than thousands.

This made me think. We have various options when it comes to open-source replacement software such as OpenWRT to run on routers, but I haven't been able to find any equivalents for lower-end switches.

Are there any projects out there that supply replacement SDN-enabled firmware for cheap home switches (such as the Netgear GS724 range)? (I don't need fibre, or 10G speeds - simple 100M or 1G Ethernet ports would be more than enough)

Failing that, what's the next best way of getting a network of several boxes with plenty of Ethernet ports that can run Open vSwitch/some OpenFlow-capable software? Multiple PCs, each with multiple 4-port ethernet cards in? RPis with lots of USB Ethernet ports? Wifi routers running OpenWRT + Open vSwitch?