Halloween without the hassle
I Don't Want to Spend Money on a Costume I'll Wear Once
Reasonable. Start with a different question.
What could I still use on November 1?
The November 1 Test
Before buying anything, ask whether the item has a life after Halloween.
If yes, the purchase may be easier to justify. If no, check whether a $0 option solves the problem almost as well.
Route 1: Spend $0
Use the 80% rule. If clothes and accessories you already own get you most of the way to a recognizable idea, finish there.
Route 2: Buy One Reusable Thing
If one item is missing, prefer something you could wear, use, lend, store easily or repurpose later.
Route 3: Buy One Costume-Specific Thing
Sometimes a cheap, costume-specific item is still the most convenient solution. That's fine. Just make it a deliberate choice rather than the first assumption.
When a Full Costume Makes Sense
A full costume can be worth it if you genuinely want one, expect to reuse it, the event requires more effort, or the convenience matters more to you than the price.
The Short Version
Ask “Will I use this after Halloween?” Then ask “Do I actually need it?”