Makeup brushes are key to creating a polished look. However, I have yet to purchase a cosmetic brush for more than $15. I don't think you need to spend a lot of money for brushes. You can find just as good quality as MAC brushes but for a fraction of the cost.
Some of the least expensive ones I have found that work perfectly well for me are the ELF essential eye shadow brushes, the ones with the white handles. They retail for $1 and you can find them at most Targets or even the Dollar store, and of course eyeslipsface.com.
However, not all of the ELF essential brushes are good quality. The face brushes from the line don't do it for me. They shed, the bristles are scratchy, and on one occasion the handle completely broke.
For face brushes, I have used a couple of the ELF studio brushes. My favorite is the ELF studio blush brush. However, I don't use this for blush, it's too flat. I use it for setting my under eye concealer with powder. This retails for $3 at most Targets and at eyeslipsface.com