Hi,
Regarding Jeppensen prices see
Digital IFR / VFR Charts for Your iPad - Jeppesen Mobile TC | JeppDirect Aviation Store
As far as I can gather you get the serial number if you purchase Jepp View,
see
Electronic Charts for prices. There are links to European maps too.
Note, I am far from an expert on this, although I am interested in looking into using the iPad myself also.
Also, I see from AOPA that the FAA has authorized a US Jet charter company to use the Jeppensen option
AOPA Online: Jet charter to use Jeppesen iPad app in lieu of paper charts