Somehow, I think the market is thr better deal...
Unless you're looking to do anything other than stockpile, and eventually trade, the stuff at the hardware store isn't going to be as pure, or as readily available in the same bulk amounts. Plus, once you "invest" there, they expect you to physically take the stuff off their property, and onto your own. For the non-smiths amongst us, as well as those not stocking up for a post-apocalyptic general store, I don't see the use.