What is the worth of a soul?

I have to record something funny Boston said yesterday. He got ten dollars for reading one of his books, and as he was seperating his money into tithing, mission etc, he started to count up his mission money. He had saved and additional 54 dollars to put in his mission account. He was feeling pretty good about that, and then I told him I proud of him saving for that, because he is making it a priority, and he'll be glad when he is older because its expensive to go. He asked how much, and when I told him it was about 10 thousand dollars, he had a look of disbelief in his eyes. I said, "Isn't that a small price to pay if you can save ONE soul?" He looked at me and said, "Well, maybe two souls, but not one!" I tried not to laugh!