OpenWrt switches

The HPE or HP 1920 series are some cheap options for used gigabit switches with external console ports. These were produced by a Chinese part-owned HP subsidiary "H3C" which they acquired when they purchased 3Com and sold by HP and later HPE.

GPL sources aren't available (despite requests!) but nevertheless many models have mainline or snapshot OpenWrt support.

The PoE models aren't fully supported (e.g. fan speed control is lacking so the fans default to full-speed and the stock fans are noisy on full power), but development is active and ongoing. Some models (non PoE up to 24 port) and the smaller PoE models do not have fans so that's not a problem. Link aggregation doesn't yet work on any Realteks in OpenWrt as far as I know.

Locally the 24 port (+ 4x SFP) non-PoE version is available used from about £20 (€25 / $25).