I've owned 3 Jaguars since 2003 - 2 X Types, and, currently, an 06 S-Type VDP with the 4.2 V8 in it. I have not found them to be especially expensive to maintain because I do all my own service work on them. The X-Types was derived from the Ford Mondeo - and - shares some parts with it - about 20%. The X uses either a 2.5 or 3.0 AJ series V6 based on a Ford Duratec, but, well massaged by Jaguar to deliver up to 227 HP. If you decide to shop for one - find one that has been well taken care of (service records, etc.), and, equip it with an extended warranty if expensive surprises bother you. Also - buy the newest model year you can, because Jag continued to make many improvements to these cars during the model run. The 2002 models are the cheapest, but, also, had the most problems.
Hope this helps:
Regards:
Oldengineer