I was resigned to purchasing white satin at a big box store and making an one-use collar. But, I scored 4 yards of white poly satin for 99 cents at the ARES thrift store.
I laid the front and back pieces of Kwik Sew 2555 (the pattern for the top) together and traced the shoulder line and around the neckline. I used a saucer to draw round shapes--3 in the front, 2 in the back.
This is a technique often used in machine applique. This left me a dilemma. In machine applique, we snip the underside lining to turn the piece right side out. The open cut side is then applied against the backing so that it never shows (or frays).
How do I close the cut opening on the collar so that it doesn't fray, stretch or tear? I eventually used a carefully-placed piece of fusible interfacing under the hole and tweezers to hold it in place while I ironed it in place.
I sewed snaps on the back collar edge and then called it done.
This is the only part of the costume that won't have a post-Halloween afterlife. It's pretty small and made from scraps. I won't lose any sleep over the waste.