Well, I saw when Cheapy was in Malmö that they had granite slabs. Bauhaus also has them, but they are different types of gray shades and aren't really marble but crushed stone.
The thing is, we've ordered kitchen countertops in black granite and also ordered for the windows, but I think overall it's too much with an extra five thousand for three windowsills. Sure, it looks nicer when it's uniform with the same stone in the windows and as the kitchen counter, but I think black marble looks even better and blends in well.