I have the same questions as Suz.
Why on earth would he be going to the prom if he isnt attending the school? Is he doing the GED program? Even then I cant really see him doing the prom. Is he dating someone from the high school exclusively?
Honestly with his current behaviors as far as the inconsiderate way he is treating the family, I wouldnt be in a hurry to treat him to the prom. He has court fines to pay. That is more important than a tux.