I spend an outrageous amount of time looking at fashion I can't afford. Designer clothing is not cheap. There's no way around that, unless you are a model or fraudster or something. I usually only purchase high end brands during end-of-season sales. Designer clothing is expensive for a few reasons.
Firstly, you are paying for a piece of well designed, quality, in-season clothing from a high-end brand.
Secondly, Designer brands have a standard of quality to live up to in the production of there ready-to-wear clothing. The quality of the materials used is very important. There are months devoted to sampling and testing different materials for a collection. Buying a large amount of fine materials is very expensive, which contributes to the retail price. Manufacturing is also a huge factor in the process. There are many, many costs in manufacturing that contribute to the retail price. Like most mass produced clothing, certain pieces will be manufactured by cheap, lower skill level factory workers. However most designer clothing is made by skilled workers who are well trained at their craft, and well paid for their work. For example, Louis Vuitton manufactures their ready-to-wear lines in France and Italy exclusively. Manufacturing in a developed country with skilled workers is very expensive for a brand.
Thirdly you are paying the mark-up price, as well as the substantial amount of tax added to the marked-up price. First the brand applies a mark-up to the wholesale price of a piece of clothing, then retailers apply a retail mark-up to the wholesale price. The retail mark-up for brand-name designer clothing is typically around 2.3x. This mark up insures that even if the piece of clothing were to sell at 50% off, the retailer would still turn a profit.
Personally, I can only justify buying a piece of clothing if I know it is well made. I'd rather have a few quality pieces than more, cheaper, poor quality pieces. However, there are more affordable options that I like. For example, some inexpensive brands I like are Topman, Uniqlo, and American Apparel. I do a lot of vintage shopping as well. It's cheap, fun, and sometimes you find some really nice clothing.