I think the best thing to do is wait for the prices or the market to be stabilized before buying. The reason is if you buy now and the prices are still going down it's a loss for you so it's better to wait than to have loss. So, you can't tell if it's a great opportunity.
Low price due to retracement or because of bad news is really a good opportunity to buy or invest. But before deciding to buy, you still have to analize market trend or price movement about further dropping in price. After you are sure and you find a strong buying signal that you have to buy soon at that price. This is a wise decision to buy or invest.