Charles Spurgeon Commentary 1 Chronicles 21:24-25

"And king David said to Ornan, Nay; but I will verily buy it for the full price: for I will not take that which is thine for Jehovah, nor offer a burnt-offering without cost. So David gave to Ornan for the place six hundred shekels of gold by weight." — 1 Chronicles 21:24-25 (ASV)

And king David said to Ornan, Nay; but I will verily buy it for the full price: for I will not take that which is thine for the LORD, nor offer burnt offerings without cost. So David gave to Ornan for the place six hundred shekels of gold by weight.

Not paid there and then, for he did not carry that amount with him, but fifty shekels of silver were paid that moment to bind their bargain, according to the narrative in 2 Samuel.