HEP deals with the study of fundamental particles and their interactions. This includes fundamental particles of Standard Model like quarks, gluons, W and Z bosons, neutrinos, electrons (and other leptons) .... and of course the Higgs Boson.
However, when studying quarks and gluons, we are also trying to understand information about protons and neutrons for example. Things like this collide with nuclear physics where the domain is focused on these sub-atomic particles. At the same time, particles like neutrinos can be created through nuclear reactors, created in the sun or have origins from super novae and neutron stars as some stars die. So, the domain of HEP penetrates into nuclear physics and cosmology sometimes. Hence, HEP experiments have scope from quantum level to cosmic level.
At the end of the day, HEP experiments deal with fundamental particles but sometimes the physics goals align with experiments in nuclear physics and cosmology.
Doing HEP experiments is not cheap. Currently the US (in collaboration with South American Nations, India, Japan), Europe (with collaboration with India, Japan etc), Japan, India and China lead the front of HEP experiments. HEP experiments are not cheap to come by. It requires years of planning, a physics case, demonstration of viability of an experiment in large scale, sustainability over decades and growth of community with computation and hardware related innovations as it happens.