A.P.
Ok, this may sound super corny but, it was the first thing I thought of!
Did you ever see the Cosby Show epsiode where Theo came home w/ a bad report card? He told Cliff he wanted to be "regular people"? So, Cliff pulled out the Monopoly $$ and asked how much Theo thought "regular people" made. After that, they just went down the line of everyday real life expenses and Cliff took $$ away eventually leaving pretty much nothing for "fun" stuff!
Does you teen have a job? Use that paycheck for the Cosby Show experiment. If he or she doesn't, go to McDonalds or somewhere and ask the Manager what you earn!
Maybe that will be enough to show your teen that trying to live life on your own w/o at least a high school diploma is a hard life!
I hope I've helped. Good luck, and I'll remember you for when my kids become teenagers! :-)