“life.” The Hebrew word is nephesh (#05315 נֶפֶשׁ), often translated “soul,” and here it refers to human life. The redemption payment for a human life is costly. So costly in fact that no sinful human can pay it, it had to be paid for by the innocent blood of Jesus Christ, God’s only begotten Son, the second Adam.
[For more on the meaning of “nephesh,” see Appendix 16: “Usages of ‘Soul.’”]