Aftermarket head unit is definitely cheaper and can include Bluetooth, DVD, HDD storage, and navigation. But, I'm still planning to go with the 730N because it includes hands-free, navigation, HDD storage, AND satellite radio. I couldn't find an aftermarket radio that includes the satellite radio.
As far as the mirror goes, I like the OEM option. There's quite a few on eBay. I got mine for $40. Because the OEM mirror is tied to the bus via the pre-installed cabling I found in the headliner, it turns off the auto-dimming whenever the vehicle is in reverse. So, even if the lights are on in the driveway, I can back in or out without looking through sunglasses (so to speak). Then, the auto-dimming turns back on once I put the truck back in either Park or Drive. I don't know if you can do that with aftermarket mirrors.