The W7 Face Blender brush (£4.25 from Fragrance Direct) is a purse friendly solution to your highlight and contouring needs.
If you struggle to get the perfect contour or highlight placement, this brush is a godsend. Loading it up with my powder of choice, I run the brush along the fullest part of my cheeks so that the depression in the brush runs along the high points. Depending on which way I hold the brush, the tightly packed dense fibres deliver the perfect placement of highlighter or contour which you can then blend to perfection with a softer brush.
It makes a somewhat tricky technique as simple as can be and super quick too!