I have read and heard both good and bad things about EzCosplay.com and another one or two that I cannot think of, as far as manufacturers go. There are a few others as well. Biggest thing with these types of sites are usually quality or materials used. Most seem to be hit or miss with quality and sizing. There are a few other online sites that are hit and miss as well.
A commissioner should give you a better quality product, though generally more expensive.