Hey there,
Well I may be wrong (I am sure that I will be corrected if I am) but I believe that the initial Class1 for JAA issue has to be done at Gatwick HQ. I think mine cost about 240GBP when I had it done.
The other thing to think about is that you will not need one till you start the flying, so if you are doing only the the exams at the moment you may as well wait till you start flying till bothering to get the medical.
Hope this helps sure more will be added by others more in the know than myself.
-273