fabbe92,
it's a good idea to have your medical status checked as early as possible. You have mentioned it yourself - there is no point in pursuing your goal when you aren't eligible for a class 1 medical in the first place.
The costs for the yearly examinations are relatively low compared to the initial examination. I had to pay around EUR 500 for the first examination, and I usually have to pay something in the region of EUR 100 for the yearly revalidations. This, however, might be different in the UK.