First, as pointed out, having a kidney removed is major surgery and puts the donor at risk.
Second, profiting from kidneys seems rather unseemly. For someone to make 150,000 profit from this scheme does not seem above board.
Third, if there is a waiting list for donors, and one pulls shtick to get himself to the top of the list, that may be alleviating his own pikuach nefesh, but increasing the pikuach nefesh of someone else who now has to wait longer.
Fourth, if we allow organs to be bought and sold, it will increase the chances of violent attacks by people looking to steal somebody’s organs.