The year my daughter wanted a Skeleton Costume, I was not impressed at all with the store costumes as it involved more cheesey glow in the dark stuff instead of anything even coming close to real. Instead I purchased black sweats, 1/2 a yard of white material, some stitchery witch, a white knit hat, black knit gloves, white fabric paint and facepaint.
Using a template from the internet, I made a pattern and cut the bones out of the white material. I did this for front and back. Using the stichery witch I ironed the pieces onto the sweats to make up the main part of the costume.
Using the fabric paint, I painted hand and finger bones onto the black gloves.
We tucked her hair into the white hat and painted her face. Her costume turned out great and she was the envy at school, even among the other skeletons, because she was the only one to have bones on the backside of her costume.
Total cost: $30