There are a lot of things to factor in. But I am going to assume we are talking about a level playing field. Not one where you have the 6 WAR offensive first player like Stanton compared to the 3-4 WAR defensive first player like Ender. The pay scale on those players will never be the same. You are going to get more bang for your buck with the defensive first player.
With that being said $$/WAR holds strong to around 3 WAR and then starts to diminish. You will pay less money per year on the open market for your 6 WAR player than you would for 2 3 WAR players. Also factoring in that giving that money to a 6 WAR players open up a spot on the team that you would hopefully fill in with a pre-FA player that would clearly cost less than what he would produce on the field.
Please. Learn. To. Read.
The discussion was specifically about prospects, not MLB veterans making tons of money. The thread literally has the word "prospects" in the title. Harry specifically asked about which type of prospects a team should prefer.
Jesus man, get a damn clue just once before jumping in to contradict someone. Just once. Please.