The JHP Package costs roughly around your first borne child, a night with your wife, and a deposit on a Sydney home.
(Around $2000 for an Omega Unit, and up to $5300 for the HSV with Sat Nav and Gauges).
You can get some money back ($250) if you return your series I colour LCD headunit back to them, however you can get MUCH more if you just sell your series I head unit on eBay..
My suggestion is to get an IQ unit from a wrecker, and get the required trim pieces from Holden.
If you get a model from an Omega/Berlina/Calais, which are the same silver colour as Series I models, then you do not have to go all out on buying the gloss/piano black trim pieces, which saves you lots of $$$$
To give you an idea of prices, an SV6 IQ unit, complete with trim and a DZ HVAC module (Which requires modding if fitting to a Single Zone HVAC model) went for around $600 a couple of weeks ago.
So all you would need to do is pay someone to program the unit (With your VIN number, and all the fun stuff I mentioned above), modify your wiring to suit, and viola, IQ system for less than half of what JHP is selling.