First of all, which version do you want to do? Harley has a million costumes nowadays.
There are tons of great commissioners on this site and DA for things like corsets and bodysuits/catsuits. If you're planning on buying lots of pieces rather than making, you should try and figure out a budget. Can you find boots that work at Goodwill, or are you willing to drop $200+ on kick-ass goth boots? Corsets are expensive, too, with good overbusts with steel boning STARTING around $250.
I did my own version of an AA Harley ages ago, using a black/red corset I already had ($250), some dollar store gloves, a buttondown I already had ($15ish), a wig I had ($40), stockings ($10), and made some petticoats ($15). If I had completely started from scratch and wanted to use that particular design exactly, I would've spent a LOT more time and money than the $40ish I spent on new materials and facepaint. It's important that you decide what you want to do, and what your budget will handle!