Obtaining an IQ unit is the tricky part. (Well obtaining one for a decent price is).
The first one I got was from an Omega (So it didnt have Sat Nav, diversity antenna support, and CD ripping support).
I got that for around $400 with some trim bits. (The wrecker was a pain in the bum to deal with).
I didnt fit the Omega unit, as I had Sat Nav, and I didnt want to lose this function, so the Omega IQ unit sat around for a bit...
The HSV IQ unit cost ummmmmm, more than it should have. (Lets just say there wasn't much change left out of $3K).
Luckily I sold my old Headunit, the Series I Sat Nav, some trim bits from the IQ unit that I didnt need, and the HSV E2 Gauges for close to $2K (So the upgrade cost me around 1K all up).
That included pretty much all new bits for the center console. (As the HSV E3 stuff only comes in black, and it looked a bit weird having the light urban (Beige) console bits.
Having said all that, I have seen Calais IQ units go for around $800 - $900 with some trim bits (And Sat Nav).
There was an IQ unit from an SSV (with Sat Nav) that was selling for $1100.
There are also a few hidden costs with upgrading to an IQ unit.
1) $350 - Programming. (You need to have the VIN number on the IQ unit programmed to match your cars VIN, but while you get this done, you may as well ask the programmer to enable EVERYTHING on the IQ unit)
So you can have a reverse camera, the Rear Seat DVD player play audio and display video on the front screen whilst driving (Video In Motion), Change the Startup Screen (HSV, Holden or Chev), and do a firmware upgrade too.
2) Video - $150 If you want to use the video input, you will need to either source the connector from a wrecker, or buy one that plugs in to the IQ unit (at $150 a pop)
3) Wiring Adaptor - $150 (The wiring plug is the same for Series I and Series II models, but the wire locations are completely different. So you need an adaptor to convert the S1 wiring to work with the IQ unit)
4) Trim Bits $$$$ (Depending on how terrible the wrecker is, you will probably have some broken trim bits, or will need to purchase stuff that is missing. This is what caused me a lot of grief
5) Series 2 Cluster - $300 and up (Note this is only really needed if you have Sat Nav, as the Series I cluster doesnt work very well with the Sat nav prompts and data. (It works, but is a pain in the bum to live with).
^^^^^ I still need to do this step, and I am going to try and fit a Grange cluster up and get that working. (Which is going to be more pain in the bum)