I 'm using a Creative Zen (2 G

Mp3 player hooked up to 2 active speakers and 1 active sub woofer.
- 2 x Active Speakers affixed under the roof right behind the windshield
- 1 x Active Sub Woofer under the Front Passenger Seat
- On/Off Switch for the speakers affixed on the Dashboard
The sound is "ok", I mean you can't compare it with any top of the shelf setup. But at least I can still enjoy the tunes driving with the windows down both on and off the road and carry whatever full load or 4 passengers as I need in the back. Power consumption wise is not that heavy a load so I'm still running off a 40AMP Alternator with 45Ah Maintenance Free Battery.
Cost wise is pretty economic I'd say.
2x Active Speakers = USD 30 x 2 = USD 60
1x Active Sub-Woofer = USD 180
Audio Cables, 3-way Audio Jack Adaptor and a On/Off Switch from any electronics shop at around USD 15
Creative MP3 Player (Bought it 2 years ago when first released) = USD 60
All in, USD 375.00 (Compared to USD 1,000 for a Basic Boom Box Setup with Head Unit in most audio shops around here in Jakarta)