You just don't get the politically correct view on this, Lincoln offered to buy the slaves. That makes all southerners bad people, because we didn't sell them to him and end the war. Because the War was only about the slaves. That would have fixed everything and we could've rejoined the Union and made nice again. Even if Lincoln could have bought the southern slaves, the question of status regarding the Independence of the Southern States themselves from the United States still would have been on the table.
Lincoln started the War to force the Southern States to remain in the Union. He even contended that they never "legally" left the Union. Hence his false contention that the Southern States were in rebellion, therefore allowing him to conduct the war under the U.S. Constitution. Others today still fight that Indivisible Union argument, even when secession was clearly thought to be a legal option of the states by the learned judges of that day. So, How does buying Slaves for whatever amount of money, Or for that matter if the South had simply freed all the slave on their own, how would that have solved that little problem of Southern States independence? It kind of like the old WW I song "How are you going to get them back on the farm, after they've seen Paris".
One has to wonder how committed to this plan Lincoln was? Or was it simple another of his political gambits?