Melbourne was shopping Jones around last year, and then the Brock trade emerged.
Every player has their price. If Carlton said you could have Judd for Jones, you would take it. So, just work back from there until you get to Jones' value. I tip you'd be working for a while, because Jones, while a hard worker with ever-improving disposal skills, is a long way short of top line.
Melbourne have concluded that Jones, while limited, has value. They would be mad not to consider trades.