You want a fishnet/mesh shirt? Get those halloween costume tights, or others that are on clearance. You cut off the toes, cut a hole in the crotch, and that's your shirt. (Psst! You can also use striped tights for this.) I like the Halloween costume kind because they are usually all fishnet without the more solid upper shorts bit regular tights often have, and they're usually way cheaper even when they're not on clearance.
Get cheap black clothing, bleach, and cheap paintbrushes or cotton swabs (or a bleach pen). Put a layer of cardboard between the layers of fabric and paint whatever you want on it with your bleach. (Search for "bleach painting" for more detail and inspo.) (I think some people use spray bottles bottles, too, but I've never tried that.)
Add safety pins to everything. Hell, string them together into a necklace and dangle charms from individual pins.
Get your black lipstick (or other uncommon color, like green) when halloween makeup is out. Wet n Wild often have fairly inexpensive products, and they're pretty good quality in my experience. (Plus sometimes you can find them on clearance even cheaper.)
You can get chain from the jewelry making/craft section and diy jewelry, or add chain to belts, hats, jackets, bags, whatever. (You can also salvage them from things like old wallets or decorative belts made from chain, which you can sometimes find in thrift stores.) Dog chains also work.
You can also as lace trim to pretty much anything, if that's more your style.
Found something at the (thrift or other) store, but it isn't black? Fabric dye, to the rescue!
Think outside the ready-made box, my lovely creatures of the night. Experiment! Get creative! Don't be afraid of things not turning out perfect!
Also: you don't have to be in all black. Jewel tones are common, but so are pastels. Be unlimited by stereotypes, and flourish 🖤