I've made DD a couple of fairy/ballet-type skirts v. cheaply as follows:
Buy a length of wide ribbon and a piece of net fabric twice the length.
Fold the net in half (or use 2 contrasting colours and make 2 layers) and sew onto the middle of the ribbon, gathering it as you go.
Fold the ribbon over and stitch it down. You now have a tutu type skirt that you can embellish as you please (ribbon = waistband, you tie it in a bow around your DD's waist and no-one can see the join), I got some little rosebuds and some sequins from a craft shop and scattered them all over.
She wears it with a vest or plain t-shirt - I did get her some wings from a stall at Glasto and a wand from Claire's, though, as they would be hellish to make!
Pirate? Striped top, black waistcoat (can make quite simply, no great sewing skill required, bandana and black/red cheap trews, cut /\/\/\/\ along the bottoms? DD likes being a pirate...
I have attempted to make her a princess dress but quite frankly the ones in the shops are not bad and unless you're a whizz at sewing/have lots of money to buy fabric and trimmings, it's easier to buy them.