2 Samuel 24:21-24

21And Araunah said, “Why has my lord the king come to his servant?” David said, “To buy the threshing floor from you, in order to build an altar to the Lord, that the plague amay be averted from the people.” 22Then Araunah said to David, “Let my lord the king take and offer up what seems good to him. Here are the oxen for the burnt offering and the bthreshing sledges and the yokes of the oxen for the wood. 23All this, O king, Araunah gives to the king.” And Araunah said to the king, “May the Lord your God caccept you.” 24But the king said to Araunah, “No, but I will buy it from you for a price. I will not offer burnt offerings to the Lord my God that cost me nothing.” So David bought the threshing floor and the oxen for fifty shekels
A  shekel was about 2/5 ounce or 11 grams
of silver.
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