some piece of metal to increase their height wont cost 50m £ pound.. :-/
I have passed your quotation on to HM Government and you start next Tuesday. Please bring a welding torch and 368 lengths of 10m steel.

seriously that job can be done with very minimal costs in my country that you cant imagine.. 8-)
and if thats a job offer, I will need health insurance

in oil wells we use #1 quality steel for drilling for the equipment and never costs like that.. I'm an engineer (have a degree) in the related field

The problem here, Cem (as I understand it), is that the weight of the windmills is causing them to sink, so adding extra metal will have little effect and may, indeed, exacerbate the problem. I would guess (as a layman, not as a civil engineer) the only thing they can do is to sink piles down many, many metres into the seabed, fill them with concrete, and then secure the windmills to these new foundations. All-in-all, I think that would be costly.
But, as I say, I'm only guessing. :-/