What’s the cheapest scientific instrument that can get an average amateur to the bleeding edge of discovery work? So not just scutwork that the pros with billion dollars instruments like CERN or Hubble indulgently farm out.
There’s always been grinder tasks like variable star period tracking that has been available to masses of amateurs with low-end tools, lots of time, and a sort of eager sincerity. But I think increasingly, stuff with nontrivial likelihood of big impact is accessible….
…but almost all of it is computing opportunities with publicly released datasets. Primary experimental work with instruments is still I think always the preserve of the most expensive equipment.