just because their cheap doesn't mean SOME of the parts are any different than others. just means the seller either bought in bulk, or got a really good deal on a specific amount of something because it could be an old model. I bought Tein s-tech springs on ebay for about 15 bucks cheaper than tein's website. also got some kyb gr2 struts on ebay about 25 cheaper for the pair than kyb's site. their working great, only have about 3,000 miles on em but so far so good. it's certain things like lip kits, lights, and some motor parts that are going to be Taiwan knock-offs that really are made with shitty materials and assembled like crap. honestly, the best thing to do it buy name brand, but get it on ebay. that way you may be able to get the original warranty through the manufacturer and it'll be a little bit cheaper than the manufacturer's website.
a good website I found that is actually on the header of CC is velocityshop.com. they sell some stuff cheaper than the makers own website and they have multiple makes for everything.
If your on a budget just buy everything Megan Racing, from what I've heard, most things are just as good as some of the more expensive stuff, like headers and suspension stuff, but it's not necessarily the best stuff out there obviously because the price is lower.