My Melody is an easy character to be for halloween because you just need a pink dress and bunny ears. If worst comes to worse, then just tell everyone you are a pink bunny.
This could also be a good best friend or couple costume because there is a second character called kuromi that my melody is friends with. They are also dating.You could also be tinkerbell by wearing a bun, a green dress, some fairy wings, possably elf ears, and some platform shoes.
This could be a friend costume because peter pan and tinker bell are besties.
a cheaper and easier costume could be a care bear, they are simplistic but cute costume, with minimal effort.
Finally, you could be velma and daphne for halloween. you dont need a bob, but simply wear the colors they are wearing.