Now when you add 4 brushes to your cart from the shop you can get another 1 for free! That works out to $3 for 4 brushes. The deal is cummulative, so if you buy 6 you can get 8 brushes or put more simply, every fourth brush is free. Just keep adding and the cart will add the discount automatically.
The best deal is still the All Brushes package which will give give you every brush in the shop, plus any new brushes published in the next 30 days for only $10. Currently that works out to 42 44 brushes for $10, or 22 cents per brush!