“in the parcel of ground that Jacob bought from the sons of Hamor the father of Shechem for 100 qisitah.” This transaction is recorded in Genesis 33:19. The Septuagint took the qisitah (a unit of money the value of which is no longer known) as the value of a lamb, but there is no way to verify that.
“and they became.” This likely refers to the bones of Joseph. Some commentators say that the plural “they” actually refers to the plot of land (singular), but the Hebrew text is plural. The bones of famous people were highly regarded and thought of as important property which is why places such as the burial plot of Abraham is still known to this day. There is no specific textual reason to ignore the plural “they” in the Hebrew text.