Anyone who cosplays with passion knows that it can get expensive. It can sometimes be difficult to know when it's worth spending money and when to be frugal and cut costs, because we want great costumes, but we don't want to overpay. If you want to splurge on that costume and make it as gorgeous as money can buy, I think you should do it. Most people, however, need to budget, so it pays to know what to pay for. Here are some tips I hope will help:
Spend on durability
This is an issue of cost up front versus cost over the long term. If you're only planning to wear a costume once, don't spend a lot of money on making something stand the test of time. But if you're planning to wear a costume enough to wash it and travel with it, you'll want to put some money into making sure that it's durable. Because of this, I think products like Fosshape, Worbla, Wonderflex and the Smooth-On casting materials are, over the long term, a better value for your money than cardboard and craft foam. Repairs cost time and money, after all, and there are some things you can't fix in time for a convention if it breaks in your luggage.
Spend on safety
Safety first. Always. So spend the money to make sure that things around your neck, eyes, and vital organs are safe. This includes tight-laced corsets. I see a lot of ill-fitting corsets at conventions, and while I own those $30 special cheap corsets myself, I don't plan to wear them all day. Pain isn't pretty.
If a costume piece is around your neck, invest in proper breakaway fasteners so you don't get choked. It's amazing how easily capes get caught on escalators, car doors and people passing you in crowds. Baby strollers are a special sort of doom. I've been throttled enough times that now all my capes affix with heavy duty snap fasteners to the shoulders of my costumes, not around my neck. If someone steps on my cape, it will snap off instead of pulling me to my doom.
Another item that you shouldn't skimp on is proper shoes. Convention center floors are often solid concrete and the aisles aren't carpeted, so your feet are going to take a beating even in good footwear. Inflexible materials and poor support make cheap shoes, especially heels, a bad idea. Some cosplayers like Monika Lee even buy used shoes so they can get better quality, already broken in, for a cheaper price. I didn't know about the importance of quality shoes when I was younger and my feet are now destroyed. Proper shoes aren't a luxury. They're a health concern.
Spend on your skin
Cheap cosmetics applied with unsanitary applicators ruin your skin. If a product is not made for a human face, then it shouldn't go on a human face, and that includes "non-toxic" children's paints and glues. There's a huge difference between a product not poisoning you and a product that will preserve the condition of your skin, so don't go shopping for makeup at the dollar store.
Also avoid the Halloween make-up sold at thrift stores. There are rarely best-before dates on those products, so you have no idea whether that grease paint you're buying was made a few months ago or years ago. Chemical compositions of cream and liquid based makeups do change over time, so you want to know when it was made.
Preserving your skin is equally important with adhesives, and for this reason, I despise spirit gum. Spirit gum contains alcohol, which can burn both your eyes and skin. It's also flammable. For only a few dollars more you can get a proper prosthetic adhesive that works better and is far gentler on your skin and eyes. Banish spirit gum from your makeup kit! It's a horror!
Now this doesn't mean you have to buy the most expensive product out there either. Many mid-range cosmetics available at the drugstore are perfectly fine. As a general rule of thumb, cosmetics marketed to pros have significantly plainer packaging than products pushed to the public, so skip stuff in fancy bottles.
Save by buying local
When ordering online, pay very close attention to the country of origin of the goods. This will sound bizarre, but it's cheaper for me to get something shipped to Canada from China than the US because of the way that the packages are processed. Taxes are unavoidable, but the brutal brokerage fees are things you can dodge.
While it may seem more expensive to buy from a local supplier at first glance, keep in mind that they're absorbing those shipping and brokerage fees, which are much lower than the ones you'll end up paying. Depending on where you live, local vendors may be hard to find, but ask around because it can save you a ton of money. Also, when doing web searches, include your country of residence in the search terms to save you time narrowing down the closest vendor.
Save on mass-produced props
You don't have to make Thor's hammer, Storm Trooper helmets, or Batarangs anymore: there are so many good mass-produced items out there that are high quality and that will still save you money. Again, economies of scale mean these companies can make these items for significantly less than you can. But there are also people online selling various prosthetics and props which will save you money because you don't have to buy the casting materials, which are often sold in sizes far larger than you'll ever need for a small project. When you buy a finished piece, you're only paying a fraction of set-up costs, and labor is minimal because it just comes out of a mold.
Save on fabrics when possible
There's a conceit among some cosplayers about making your own costumes from scratch, right off a bolt of fabric. The thing is, this is often the most expensive way to do it. If you can buy a piece off the rack and just do a few alterations, it's a better use of time and money. Mass produced goods benefit from economies of scale, so the entire garment likely costs less than the raw fabric you'd be able to buy by the yard. I am obsessed with raiding remainder bins for cheap accent fabrics, because I don't want to get stuck paying fifteen dollars for a half-meter of gold fabric to finish an edge.
Another trick that many savvy cosplayers use is buying cheap prom gowns at thrift stores for the fabric. You can often get significant lengths of otherwise pricy material from the skirts. Rip the seams out and ta da! Cosplay fabric! I once scored four free gloriously poofy silk bridal gowns from a hair salon because the bodices had been damaged by hairspray and they were looking to get rid of them. The skirts became parts of steampunk outfits.
So let your family and friends know that if they're looking to get rid of any sort of formal wear, you want it! It's great for re-purposing for costumes! Even if you don't use it where someone can see it, it's perfect for test runs when you're tweaking a pattern. "Muslin" mock ups of costumes may seem time consuming, but experienced cosplayers know that they save you time and money in the long run and lead to a better finished product.