IIRC £40/£50 per wheel.

As said above you will not be able to use wobbly bolts for an 8mm change in PCD. Your best bet is PCD adpaters which they do (or did) or get them to drill your wheels if they still do them. To convert from 4x100 to 4x108, they will bore out and mill slots on two opposing holes. Two holes will remain untouched as they would be in the right place.