Can't quite remember but used a cheap kit car pedal set off ebay with a bit of modification and welding ( around the £100 mark, brought a few years ago ). The caliper is just a mini pit bike one, again a cheap one off ebay. The control board I already had but is a Leo Bodnar board. The rest just bits and pieces from the parts bin in my man cave lol.
Fairly easy to build but took a few mods to get roughly right. Not perfect in my book and I know where I would improve, but were my first build down the hydraulic brake route as a prototype and function pretty well. I would guess fairly straight forward for anyone with some mechanical experience and can weld. I know where I would improve and would probably build my own base pedals next time rather than buy a set so I can enhance the mods that I have in mind for them.