I am interested in flying from the US to Poland in September, via London. There seem to be many inexpensive options from the US to Gatwick on major airlines and many cheap flights on minor airlines (SkyEurope, RyanAir, EasyJet…) from other London-airports to Krakow.

My question is, exactly how difficult and expensive is it to travel from Gatwick to Luton or Stansted airports? Also, would it be necessary to book a bus/train in advance or is it reasonably safe to wait until I get to London?

Thanks!

Jim