snork: I believe that your lecturer is getting directly either from the supplier, or buying in a larger amount (bulk) due to the number that he have to handle (lab coats). As for the photocopy shop, obviously they do need to earn as well, else if they were to sell you at the cost price, how are they going to pay their rental =/

Well, I believe that you should have consulted your lecturer first, before making any decision, especially when your friends told you that you could get at a lower rate. However, you chose not to consult first, and buy straight, therefore I think it's you to be blamed.