You could always keep your original policy till Dec to make sure you don't lose out on that, but buy yourself a Cab and then insure it as a classic with restricted low annual mileage which should cost less.
Have you looked at getting a lower powered non-GTI cab ?
They did make them with 1.4/1.5/1.6 and 1.8 carb engines. That way you could buy one with less power, but cheaper to insure, then you could either work on the performance later when insurance is cheaper or change to a GTI Cab later.
