when I don't wanna dress up to much I wear black jeans with a zip up and a band tee or any random shirt. something to keep in mind is in the 2000s people wore a lot of tight fitting clothes but if you don't wanna it wont effect the outfit a lot + if you go to thrift stores around holloween they might have things like fishnet gloves or other neat accesorys depending on wear u live
not exactly the question but your hair will change the sorta "vibe" of the outfit and depending on your hair you could look a lot more grunge, however dressing like how i described is easy and you don't need to buy a lot of expencive things
clothes with stripes, big bows, and studded belts were pretty big in the 2000s as well
plz ignore my spelling