The problem is that I indeed calculated wrong, when I said it will be 40% increased costs. When the project started I wanted to buy a complete device, because I'm not so keen on tinkering on my old N900. Especially because it's screen look quite horrible nowadays and I'm not so skilled in doing things like that.

After reading Bearseakers post, I must now recognize that 990 € is just for the board, so it's even more expensive then i thought on the first view.

Sorry to say that, but I think my already paid 150 € have become a donation and can't be longer seen as a prepayment.