Last time I looked the cost of Vitamin C, pure, from the manufacturer was about £5 / Kg, say $10-15 for just over 2lbs. (I needed a cost for a cosmetic product I was formulating, and was offering to buy about half a tonne a year)
Of course if you are buying comparitively small quantities that have been packed and repacked, the cost is going to be much more. $10 a pound from Amazon sounds not excessive once you factor in packing it, the packaging it comes in, packers profit and Amazon markup.
Oh and "Organic Vitamins" - My A*se.
All of the bulk commodity vits are made by huge great chemical plants to pharmaceutical standards. Usually in Germany, and by companies such as BASF and DSM (Previously known as Roche in some markets)