You can cheap out by getting one of the Z probes for a 3018 machine;
One of these.
1: Crimp some alligator clips to the other end of the wires.
2: Measure the thickness of the probe.
3: Grab a multimeter, set it to continuity. (or if you want to get fancy, you can inline a battery and LED)
4: Clip the alligators to the multimeter probes
5: Place the Z probe under the tool, clip the other alligator to the tool.
6: Lower it by 0.1mm until the multimeter beeps.
7: Remove probe and lower Z down the thickness of the Z probe and set origin.
It’s not quite automatic, but it’s repeatable for tool swaps. It was part of my CNC origin guide.