People about Cosplay...
The only place it should really matter is in competition. Don’t enter a workmanship based contest with something that you bought or commissioned, and don’t take credit for the work of others.
That said, some contests have a category for commissioned or purchased costumes, you would be fine if you entered there.
At risk of sounding like a Nike ad, just do it! Find a character you want to dress up as and get started. If you need help there’s plenty of tutorials (both blogs and videos), books, and forum you can turn to for advice, especially if you’re doing something popular. Or you can do what I did and just muddle through it yourself. My first costume I bought what items I could, mostly at secondhand stores, dyed and altered a shirt and made some simple arm wraps out of cheap cotton. I had no idea what I was doing (and no sewing machine – do your hands a favor and use one if possible) but it came out pretty well and I’m still happy with it.
These days I usually make mine from scratch, finding a sewing pattern that is somewhat close and adapting it as needed. When I can pick up patterns cheap I look for anything that might be useful and stock up. I’ve gotten unused patterns for as little as a dime before, so even if I never use them I’m not out much. I like to let other people do work for me when possible. Secondhand stores can be good for base items and even for fabric, either by cutting something apart (one of my costumes is 95% bed sheets) or if you’re lucky even plain fabric (I once found a piece juuuust big enough and in the right color for an outfit I wanted to do).
Remember you can decide how true to the source you want to be. If something is outside of your skill level or too expensive to do “properly”, you can find a way to do something. I once stumbled upon a pattern to knit Rinoa’s duster, but painting or sewing the wings on a plain blue one works too. Or you can stylize it to your own tastes. My costumes never look great, my skills aren’t at that level, but I can do “good enough”. And you’ll never be sure what you’re capable of until you try.
I think cosplay is a bit of an art form. A lot of time goes into some cosplay, especially the more meticulous, detail oriented costumes. Because of that, it’s more than just “dressing up” to me. I see it no differently than movie costumes or FX makeup in terms of seriousness. Some people even make careers into it. I assume some others are able to break into other careers like acting or the aforementioned FX makeup.
It’s not everyone’s cup of tea… and I respect that. However, there’s a lot more that goes into cosplay than what people see at face value.