A cheap alternative to the Etyomics and others are Koss earbuds. They make two different kinds, the plug and the sparkplug. I have used them both and the plug is a little better due to the round edges not snaging on the inside of the helmet as much when you put it on. $14.99 and I think they work as well as any earbuds out there. I got mine at Radio Shack

PLUG - Earbud Headphones - Koss

SPARKPLUG - Earbud Headphones - Koss