i lost my only key for my 03 s type jag. what is the least costly way to get a key

 

I got mine from Amazon for about £15-£20 and it cost me £40 to get security coded - I also had a spare and got the blank cut for £10 using the spare as a template

 

BUT...cutting a blank using the spare does not help OP since they have no spare. I dare say that likely leaves them dealing with a dealership unless they can find a locksmith that knows how to cut without the spare to work from. And that could prove as costly as just going to the dealership...

 

With proof of ownership, any dealer can get you the T Code for your vehicle to have a new key cut (providing the locksmith has the ability). There are even fewer locksmiths that gave the additional ability to program the PATS component to work in your car.

Here's a very comprehensive explanation of the keys, programming =

Jaguar Key Fob 2001 to 2009 User Manual | Key Cutting Machine