Etymology is not the measure of a word, but rather the usage. There is no reference to slave markets. Nor to price. I have heard all of this before but do not see it in Scripture. And if it be from a month old even unto five years old, then thy estimation shall be of the male five shekels of silver, and for the female thy estimation shall be three shekels of silver.
Sin is a crime - a felony.
God, the righteous Judge, cannot be bought off. You are quite right in asserting that Redemption is always tied to the forgiveness of sins. Recovery, release, has a broad range of applications. I suspect that we are in agreement here. The result is often weaving in our theology with the Word.