most definately drop the head unit idea. that is what is so great about going with the car pc. you can make it look oem very easily while having endless options and tailoring it to your taste. You're only spending the money once so the $200 saved isn't that big of a deal imho. plus you can add the radio later after you tire of your endless supply of mp3's on hand. Plus a $60 head unit is going to be crappy quality, probably break on you and sound crappy.
if it were me id look into the hd radio option that is out there. yes it'll be the most expensive option but a great option none the less (and no monthly fees like xm).
just my $.02