I have a $10 Panasonic transistor radio in a cellphone patch pocket attached to my backpack strap. I cut a couple small holes in the pocket to allow access to the volume and tuning controls. Been riding with this setup for years.

Not stereo, but works fantastically well. And because the radio is a few inches from my head I don't need to turn it up very loud, so it rarely draws attention from others. Also means that a pair of AA batteries lasts for many hours of riding.