These are some great reliable and popular sites to get inexpensive clothing items, but bear in mind that often these items will come from China and they won't be great quality, also the people that work there aren't paid very much and treated badly.
A well known site used to sell many different things from technology, to second-hand books.
Rose Gal- http://www.rosegal.com/
More expensive than She In and not as much variety but still very good.
A lot like Ebay, but with more variety, personally I consider it better.
She In- http://www.shein.com/
Great site, huge variety, only one problem SheIn outsources all of their products so the sizes are all different, you will often find that the sizes are either to small or too big.
Good site, but limited variety, there is only one swimsuit in the swimsuit section, only in white
A bit more on the expensive side, but compared to normal clothing sites, still pretty cheap.