Another collection of things that you might be interested in from eBay today. To start off with a USB LSDJ Cart + Arduinoboy MIDI Sync + USB MIDI Device. But it isn’t cheap at all.
To follow a very cheap Pocket Music Cart.
Then a Roland PMA-5, which are fairly rare these days.
Next a Gristleism for £10.
Then a VL-5 which isn’t working, but might be of use to a tinkerer.
And lastly a fairly cheap QY70.