By far the best option is buying ANY head unit you like that has an AUX input, and picking up a cable by the company Nyko on eBay. It plugs into the AUX ports, and the dock of the iPod, meaning you don't get the poor sound quality you would have if you plugged into the headphone port. Also, the level is non-fading, which is nice. So cost would be $15 + head unit, but this obviously breaks your no new head rule.
