There is no one shop to get a head-to-toe look. The main point is mixing in affordable pieces from brands like Black Scale and SSUR with more luxurious items. Boutiques like LN-CC and Atelier carry brands like Ann Demeulemeester, Damir Doma, and Rick Owens, but you'll likely go broke trying to cop multiple pairs of drop-crotch pants.
Know when to break the bank and when to save. Leather outerwear and sneakers are always good to drop dough on, because they get a lot of wear. Remember that street goth is a mix of streetwear and high fashion—you don't have to be decked out in Rick Owens from head to toe. Nor do you have to buy the same expensive shit as every other kid on the Internet.