If you need a good brush for apply powder under your eyes the M536 Under Eye Bullet Brush is a nice one. I have this and it works great set concealer with a bit of powder! Another great brush is the M173 Mini Buffer Brush. I have this and use it to buff concealer under my eyes! It works great with thicker concealers like It Bye Bye Concealer as it sheers it out and gives it a nice airbrushed finish!
Morphe brushes are quite inexpensive to begin with but with the sale the deal is even better!