The most important human cost is that many people died. When Europeans started exploring the Americas, they wanted to force their authority upon the natives there, which they obviously didn't want. Thus, many wars began in which the Europeans killed so many natives. Hope this helps!
Exploration, in the first place, was not easy and risk-free. The ones who took the job of exploring the new world actually risked their lives and many lost it.
The clashes and conflicts with Native Americans cost thousands of lives to both the side during the entire process of exploration and colonization.
The lives of black slaves brought from Africa were also at stake.
Many slaves were killed for resisting the owners.
Thus, the human cost of European exploration and colonization was huge as thousands of people lost their lives during the long course of exploration and colonization.
