You're right T2S this nonsense will always be about him until you and your son come together and make it about the two of you.
As heartbroken as I am for your son and his realization that his father cannot be relied upon this way, I am upset that the suggestion was even presented to him to rely on his father for half the $. (There may be more there, I'm just going on what was in your post).
Life finds the lessons we need to learn and presents them for us. Maybe this is a wonderful moment for the two of you to sit down and think of other ways he (with your help possibly) can get the needed funds.
Had your son had the realization before the concert became a desire of his that his dad would not participate financially in this way, he would not have gotten his hopes up and would not be disappointed. He could have made the deal with you for half on the contingency he earn the rest through chores or helping neighbors (you know what I mean, be creative). I'm not saying he shouldn't have hopes, I'm saying he should be relying on those who will support him emotionally, financially, and spiritually. IF his father can ever be more for him, he can seek a relationship as he wishes then.
Alice