So, here's me on Friday and then on Sat. I basically was trying for a Steampunky/Victorian sort of look, more trying to get the spirit then being historically accurate (plus I think full Victorian might make me fall over cause like 20 pounds of clothes).
Second, you can make awesome costumes out of separates. Let's go back to Friday.... Tank top's a cheap one from Walmart that I thought looked vaguely Victorian. Shawl over my shoulders was bought at Target because I liked the color and it had hidden skulls. Light blue skirt is going to be part of a DragonCon costume. The dark blue skirt (which is actually two skirts, I put the other skirt in between them) came second-hand from a friend. Necklace is inherited costume jewelry, as are the earrings. On Saturday, that tank top (which I own in 4 different colors because I like the style) is, again, Target. The necklace is one I wear all the time (am wearing now, in fact), and the flowers in my hair were gathered from the garden before I left. Baby Groot in my cleavage (yes, that's a Baby Groot) was bought at the con because he made me happy and stuck in my cleavage because it was a safe place to put him.
I go for separates most of the time because it allows me more flexibility. I can do much more with two tops and two skirts than I can with two dresses. The tops get thrown into my normal clothing rotation and the skirts might (depends on their length and style, I wear my Renn Faire skirts quite a bit but the Rev War one really only comes out for costuming). And here's some more examples....
DragonCon a couple years back. Rev War skirt, same corset, shirt I've had for years, cloak I've had for years (and is a surprisingly practical garment for GA).
Halloween a couple years back. Renn Faire skirt (I own two and wear them frequently), Renn Faire shirt (used to wear lots, doesn't work well anymore since I lost weight), same corset and stole I designed and knit. Oh, and shoes I still live in.
Halloween 2014. Shirt from Walmart, corset's a Renn Faire one, and I have no idea what skirt I was wearing, I can't remember. This green corset actually gets more costuming wear than the brown, but I have less pictures of it for some reason (possibly because I stink at remembering to get pics of myself in costume).
All of these outfits were more or less thrown together by my looking in my closet and going "hmm, I think this might work." It helps that my style tends towards the Victorian and Renn Faire and I costume to that. I don't really do 20th century because I don't own much that works for those styles.
I guess the take-away from this rambling should probably be along the lines of the following...
1) It's way easier to come up with a con costume if you're flexible and creative. Sure, you're much more likely to get oohs and ahs with a perfect Thorin, but we're going for easy.
2) Separates are more flexible and a better bang for your costuming buck
Sorry guys, suppose this wasn't very useful for you. Um, you can do an amazing variety of costumes with one good black suit. That's all I got for you.