I researched medical costs recently and found that a first issue JAA Class 2 would leave little change from GBP 400. I understand that re-examinations are a mite cheaper.
Don't know if this is true, but I heard that the eyesight requirements for first issue are more stringent than for renewal, so if you're approaching the borderline it could be worth getting Class 1 sooner rather than later. Of course, you'll then have to renew every six months...
On the other hand, if you do a US PPL, the FAA Class 3 medical will set you back about USD 80...