Question:  In 1 Chronicles 21:25, King David paid 600 shekels of gold for the threshing floor; but in 2 Samuel 24:24 the Bible says he paid 50 shekels of silver for it.

Answer:  There is no contradiction if you read the accounts carefully. In 2 Samuel 24, David had sinned when he sent Joab to count the number of soldiers on active duty and ready to fight (v.9). God sent a plague and killed 70,000 men (v.15).

David was told to make an altar to the Lord in the threshing floor nearby. David first bought the threshing floor ONLY.

"...So David bought the threshingfloor and the oxen for fifty shekels of silver. - 2 Samuel 24:24

Later, in 1 Chronicles 21:22, David bought the WHOLE FIELD where the threshing floor was located.

"Then David said to Ornan, Grant me the PLACE (the whole field) of the threshingfloor that I may build an altar unto the Lord."

"So David gave to Ornan for the PLACE (the whole field) six hundred shekels of gold by weight."- 1 Chronicles 21:25

The threshing floor was bought for 50 shekels of silver and the whole field for 600 shekels of gold. No contradiction!