Aluminium in bulk is about £1500 per ton at the moment. If only! We pay retail prices. Every time the aluminium moves, the price goes up. Markets, import/export, transport, wholesalers, and retailers all have costs, pay taxes, and need to make a profit. Cutting to size at point of sale costs money and the retailer has to cover wastage and off-cuts.
Quite a few legitimate reasons why stuff is sometimes sold cheaply. End of run, expensive storage space needed for something else, bankrupt stock, downsizing, urgent need to raise money, loss leading to break into a market etc. etc. If a bargain's to be had, grab it!
Dave