It would seem the OE part is discontinued now so you stand very little chance of getting it, even if you've found it listed. However here's a couple of alternatives :
https://www.rockauto.com/en/catalog/jaguar,2000,s-type,3.0l+v6,1363294,engine,timing+chain+&+component+kit,5756
I've been using Rock Auto for about a decade, mainly for Volvo parts as my model Volvo isn't well supported in the UK and the predecessor to my S Type was also better supported in the USA than here and never had a bad part from them yet.
Even with Shipping and Handling (S&H) it's unlikely to come to 400 Euros but be careful with your local customs and excise - there is usually a shipping option that is more expensive than the others and this prepays any import duty that will be charged and delivers the item to your door without going through customs and the delay and charges that will attract.
It also gets round the fluctuating exchange rate - i bought something about 6 years ago, below the threshold (on the day i bought it due to a stronger pound/£) but on the day it went through customs, the £ was weaker and it crept just over the threshold - got charged import duty and a fee for the Royal Mail to send a card telling me this and a further fee for them to collect the import duty! If memory serves it was the fuel pump for my Volvo so the car was off the road for another week while Royal Mail sent me the card, i pai and then they finally delivered. Still much cheaper than buying it in the UK to start with though!