Stacked department store sales can knock those brands down to about the same cost as a full price item from Target. A lot of fancy brands also have diffusion lines, which are lines with similarly branded (but often less well-made) clothes made specifically for stores like TJ Maxx or their own outlet. (Most outlets, and much of the stock at stores like Marshalls, TJ Maxx, and Ross, are no longer primarily factory seconds/returns/overstock; they typically make items specifically for the outlet.)
There's also second-hand. I have some expensive but not full-on designer clothes--Eileen Fisher, Lilly Pulitzer, Filson, Pendleton, $150+ retail jeans etc..--but got them all used at thrift stores, garage sales, or Ebay. They cost more than most of the random stuff you'd find at Goodwill, but generally less than shopping non-clearance at Target or Old Navy.
Alternately, people willing to pay a cover and outrageous drink prices may not be frugal when it comes to clothes, either.