For me one of the cheapest yet best investments for mineral foundation application is the "Swirly Bowl." Most mineral makeup addicts have their swirly bowl- some were found in 2nd hand shops, some at dollar stores, and even stores like Target carry good swirly bowls.
I love a swirly bowl for a few reasons. One is a swirly bowl can protect the integrity of the foundation since only the amount of foundation used in an application comes in contact with anything that is likely to cause contamination (brush which touches skin or liquid if using damp method.) Mineral makeup has an extremely long shelf life if contamination is prevented and a swirly bowl insures this long shelf life. Secondly a swirly bowl protects another investment- your brushes. The smooth sides of the swirly bowl not only loads the brush better, it prevents breakage of the outer bristles that would be cut/rubbed by the threads of the jar lid if using lid for swirly bowl.