[JavaBrewer]

Depends on what you classify as "Bang for buck". Simple music standards (CD/MP3/AUX/Bluetooth) with factory speakers - you can something for <$100. If you are talking new head unit, speakers, amp(s) then that's entirely different and dependent on your wallet. Rod over at Car Audio Innovations would the person to ask for something special.

My 996 came with a cheap JVC KD-R330 head unit ($69 at Crutchfield) and some sort of low quality amp. Runs through factory speakers as far as I can tell. It plays music from various sources and has the Bluetooth added module. Its simple to operate, does not look like the Vegas strip at night, and probably not on the short list for thieves. Nothing special but good enough for my usage.