Before investing, you should check whether he'll tolerate the headphones. Master PVDProf (also 3YO) just won't, even to watch his favorite movie (Cars). So, we read LOTS of stories, play with his matchbox cars, talk, look out the window, and have slow-to-eat snacks (e.g, raisins, goldfish, grapes), and the next thing we know, we're at LAX!

(I'm not trying to claim any high ground here. All that play is exhausting for me, and I wish he'd watch the blasted movie so I could get a break. )