I've started an online store (https://adorely.ro) with a friend of mine using dropshippers (so we don't buy stock and manage the delivery) and we're getting our most valuable traffic from price comparison sites. While there is a limit of how many visitors you can get, the conversion rate is amazing (in some cases is more than 10%) and the cost is extremely low. Adwords is not a good idea if you don't have a good lifetime value. Also we tried to increase our Facebook fanbase but the conversion rate is pretty low (still bigger than adwords).