Most costumes are cheap and made for one-time use, but there are so many alternatives from the more expensive “deluxe” costumes, to rentals, to do-it-yourself disguises from the thrift store.
Seasonal Halloween Shops
The obvious first choice is the temporary Halloween stores that pop up on every corner. They feature the most current selection of popular costumes-in-a-bag, accessories, wigs, and make-up, but they can be somewhat expensive. Spirit Halloween offers coupons for early bird shoppers via their free email newsletters.
The "big box stores", like Target, focus on the little trick 'r treaters, candy and decor. The costumes selection for adults is usually very limited. However, some party supply stores (like Party City), offer a decent selection at better prices and since most shoppers overlook these stores you'll find a wider selection late into the season.
The web offers unparalleled access to every imaginable costume and size (especially plus sizes). There are two major drawbacks: you can't try them on and turnaround can be disappointing. Stick to the larger, reputable sites. Most offer lenient return/exchange polices BEFORE the season ends. So order very early and if in doubt, order a couple of cosumes and immediately return the unused outfit.
There is a growing awareness among suppliers that we want better made costumes. Several retailers, like Grandin Road, now offer "deluxe costumes" made with higher quality fabrics, more intricate designs, and often include nicer accessories like jewelry and gloves often missing from their cheaper counterparts. (Deluxe matching shoes and deluxe hats are still sold separately.) But the prices can be much steeper – $150 and up – and availability is very limited. May be worth the price if you want to invest in a "long-term" costume.
For those of you who want to impress or have a better chance of winning costume contests, find a costume rental place. This is an affordable solution for a fancy costume that you don't have to store or wash. Many costume rentals work with theater companies, TV productions, and other entertainment industries. If the thought of wearing repeatedly "used clothing" sends shivers up your spine, relax – they are thoroughly dry-cleaned and treated with a super-Febreze type solution.
Closet & Attic Raid
For historical costumes, raid your parent's closet. You are bound to find a sequined disco blouse from the 70s, a shoulder-padded monstrosity from the 80s, or even a perfect flowery granny outfit. Make sure your family understands that you are paying tribute and not making fun of their "bold" choices of yesteryear.
Large thrift stores, like Goodwill, are a great resource for antiquated clothes. If possible, try to find the distribution point for your local area – these stores get first picks before sending merchandise to the other area stores. Selection is hit or miss, but always a great place to find shoes, boots and gawdy accessories.
The seasoned Halloweener will likely create their own costume from scratch utilizing craft supplies, old bridesmaid dresses, and cardboard boxes. You are only limited by your creativity and resourcefulness. Thrift finds are usually a good starting point. With a few appliqués, papier-mâché, and paint, the results can be glorious. And remember that you don't need to know how to sew – fabric glues (like Fabri-Tac) and hot glue guns work just as well.