If you're looking for something to wear on 5K race day during the 2023 Princess Half Marathon Weekend, consider a traditional costume from Amazon, and have a look through Amazon Warehouse for some hard-to-beat deals!
Designed to be worn on Halloween or for other cosplay-type events, traditional store-bought costumes won't typically be made of moisture-wicking performance material. For that reason I would only recommend these for a 5K race, or maybe a 10K if you're not prone to sweating a lot and chafing. Cheap Halloween costumes can also be combined with tech running gear to make them more athlete-friendly.
I found all of these costumes searching through Amazon Warehouse (select Amazon Warehouse at the front of the Amazon search bar on desktops). Since these items are typically customer returns, they might be missing the original packaging or have the labels removed, which is why they are discounted. Style and size options will also be limited -- you'll have to work a bit for these discounts! You should check each item before purchase to be sure, but typically Amazon Warehouse items have the same generous return policy of new items purchased from Amazon.
The items featured below are just a few of the options I found today, with example actual price compared to the cost for the item when purchased new. Remember that Amazon prices change frequently so you might not find the same items or price points when you do a similar search.