I had a plain ole Premium 7 head unit with not even an AUX input in my 2006, so the upgrade got me far more than just Bluetooth. In addition to BT, I got a 6.5" touchscreen, 6 disc changer, HD radio, 32gb SD card reader which I absolutely love, and an AUX input. I installed the factory mic in the factory location next to sunroof controls. The radio data displays in the MFD dash display. Plus nothing matches the sleekness of an OEM unit in the dash IMO ...that is actually a huge deal to me.
OEM Bluetooth can be done for around $200 all in, if you're fine with 9w2 and not being able to dial out from your radio screen. With 9w2, you have to use the phone to start a call, but you can still answer calls and hang up calls using your steering wheel buttons. You can stream stereo Bluetooth audio too.
But I thought the extra cost to have the on screen dialing with 9w7 and the latest 2013+ unit was worth it. All in my cost was under $350. That price includes the "AF" version radio itself, 9w7 Bluetooth module, complete wiring harness and mic, new CAN gateway module, and antenna adapter. Of course if you just go buy the first one you see on eBay or pay what BarryT is asking on the forums, it's going to cost a bit more.
I originally went the cheaper route with the 9w2 setup then upgraded to 9w7 parts. They use the same wiring harness so upgrading is super easy. I patiently watched eBay, craigslist, and the forums until I felt like I got a great deal. That is the trick.