Before purchasing a brush or brush kit, check that each brush head is soft and full. Run your hand through the bristles. It is a bad sign if they come out readily/shed or feel coarse on your skin. The handle should feel comfortable and seem solid. Keep your brushes in a protective case or upright in a decorative glass or container on your dresser, not in the bathroom, where moisture accumulates. Every few weeks, or at least once a month, gently wash them in a mild liquid detergent or baby shampoo. Do not soak them. Pat each brush dry, especially around the area where the brushes meet the handle, and lay them flat over the edge of a table or counter so that the bristles are open to air on all sides, and reshape the brush head.
I'm not endorsing this brand, but BareEscentuals offers a good selection of brushes. Take a look simply to see what shapes and sizes of quality brushes are available, and their cost.