do you think that lower prices will really lead to increase in quanity sold?
unlikely, not by much anyways (my opinion)
also, it does matter that the online shops monitor the prices of cd's sold on labels. some shops have a rule that they sell the cds of label X at a certain fixed percentage of the price the label is selling the cd's for.
lowering the price would only make the online store lower their price too
if you have the money, try to buy from labels directly, it will support the labels, who in turn support artists (no matter how much) more.