First, if you are going to start in Europe why not start someplace cheaper than the UK and use that savings to defray the cost of the positioning flight and you might consider a long flight in EUR (e.g., LHR-MCT) to get closer to your goal.
Code:
DONE 3 Price in Local Currency US$
UK GBP2869 7663
Switzerland CHF7650 7333
Sweden SEK39700 6618
Gibraltar GIP3100 6122
I'm not sure I follow all of your mileage calculations.