My son loves the Geo Trax trains sets. For about $50, you can get a few sets for a small track. Try Target or Costco. Trains run 5.99 - 15.99 or so. Then you need the Track Packs too. About $ 19.99 for that.
First of all please note that this is coming from a 15-year old male. However saying "It's just because you're a teenager" would be horribly ignorant of you.
Another thing: My general personality is not what most people expect. Most kids of my age tend to mess around and love to have fun; personal experience has made it so that I am a relatively cold and serious individual. This could probably be the reason you'll tell yourself "Holy crap, there's no way this is coming from a teen."