I found a great article with some quick, inexpensive Halloween costumes if you need one today or tonight. These are costumes that cost under $20 and can be picked up during one stop.
For example, a Witch costume needs a dress (which you may already have), a hat (under a dollar), a $5 broom, and heels.
Bubble gum needs $5 pants, a $4 shirt and $3.99 pom poms.
Dr. Suess Thing 2 needs $6.99 converse tennis shoes, a $3.99 Thing 2 t-shirt, $4.99 pants and a less-than-a-dollar boa.
They have pics to demonstrate these costumes here
For my son, Charlie, he made his costume this year. Since everything Fortnite was sold out at the store, and grotesquely expensive on Amazon, he decided to use two boxes, some spray paint and construction paper to make the blue bus (he had to explain it to me -- if you play the game, you know the blue bus!).
There are holes on top and on the sides for his head and arms. Nice job, Charlie! And this is something you can put together in less than an hour. Have a quick costume suggestion? Let me know!