Beauty dishes are great for enhancing the lighting for portraiture (hence the name) but can be expensive for occasional use. To try out the concept you can make your own beauty dish using two polystyrene food bowls, aluminium foil, and toothpicks.
Photographer Kirsty Wiseman's weblog shares how she created a basic beauty dish by cutting out a hole for her external flash in a polystyrene bowl. Fit that on your flash and cut out the flat bottom of another bowl, cover that cut-out on one side with aluminum foil and affix the cut-out to the bowl that is attached to the external flash.
To see what difference this bit of polystyrene and aluminum foil can make check the source link below.
DIY Beauty Dish - for £1 | Kirsty Wiseman via WonderHowTo