The Navman jacket price is listed on their website at around £340 list, and comes complte with the street level UK maps. If you then register the software, you'll get the full European update for free as it is released.
You can use a number of iPaq models from 37xx through 39xx range, prices vary accordingly.
Check out
TOTAL PDA for online prices that seem better than high street (ie PC World).
Prices seem to be £199 - £420 for iPaq models.
They also sell the Navman products, a whole range of them. Note only the Navman 3400 gives the voice direction commands with their software, and is of course the most expensive
You should also add a Compact Flash memory card to you eqipment list, pref 128 Mb or larger. (£33 from TotalPDA)
This slots into the Navman jacket, and allows you to store all of the UK maps without using the iPaq RAM. It's also stores them even if the battery goes flat on the iPaq.
If you want Net access as well as Sat Nav you can use the iPaq 3870 or 3970 with Bluetooth, and a Bluetooth mobile such as the Sony T68i.
You're paying top dollar here, but they equipment will allow you to use the iPaq anywhere you have coverage to surf the Net, read Email etc etc, all via GPRS, an always on system overlaying your GSM monile phone network.
The iPaq communicates with the phone via wireless Bluetooth, meaning the phone can be in your pocket/case/cupholder and still provide the data link to the web! Very very cool
And of course you can have a Bluetooth headset for the phone that allows you to talk hands free and wireless in the car, using the same Bluetooth connection. The T68i even has voice activated dialing for true hands free use
As for power, youn can run the whole lot off of the iPaq, and the 3970 runs for hours (up to 7) like this, depending on the brightness of the screen backlight, which you can set. Other iPaqs have lower battery life I believe.
However, I use the power from the Mini cig socket, and run the cable from behind the centre console, over the steering wheel boss behind the tach, and up to the iPaq.
You can't even see the cable until it gets to the iPaq (check out my pictures above) and it does not spoil the look of the car.
Hope that helps, any more questions just fire away.
Chris.