Second hand Alesis D4 or DM5 drum module, they have twelve trigger inputs to midi. (there’s an Akai trigger interface too, forget the model number)
You can use ultra cheap piezo transducers & mount them how you like.
Of course this will give you midi only outputs, not quite what Stretta is doing in those vids, as you will have no audio from the piezos to mix back in. Cheaper however than an 8x audio interface & 8 Planet Waves clips.