$15? I don't think there's anything you could buy for $15 that will get you power...of course the Honda guys would say "get some stickers!!1"
the cheapest HP mod I can think of is an intake, and depending on where you get it, it can cost anywhere from $25-$250. I got my intake for $25 + shipping. AEM and Dr Speed overcharge for their intakes (IMO).
next option would be working with the pullies, but that can get pricey too.
You really have to pay for performance.