A little consumer education. Don't compare item prices alone. Just because a retailer has a lower price doesn't necessarily mean it is going to cost you less. You need to compare apples to apples, in this case the TOTAL price, including sales tax (if applicable) and shipping. Some retailers charge a bit less for the item but charge more than their competitors for shipping. Sometimes a lot more!
Some offer free shipping when a certain dollar figure (product prices) is achieved, but in many cases this still doesn't mean you're actually paying less overall when you compare TOTALS between retailers. Those that offer such deals typically charge a slightly higher product price to offset the cost of shipping.
Retailers have one of three ways to charge shipping & handling. Flat rate based on dollars spent. A percentage of dollars spent. Lastly, actual shipping costs...those fees that you'd pay if you were to ship the item yourself...the most cost effective to the consumer but few use.
Why do some retailers charge more than others? Overhead. They have higher overhead to maintain. Ads in magazines, printed catalogs, staff, lights, warehouse and inventory. So bigger doesn't necessarily mean automatically they can offer better prices.
There are retailers who act as nothing more than order brokers. They stock little or nothing only collect orders, pool them together and place orders with the appropriate resource for the items. Get the items, then redistribute them to the customers placing the orders. Little if any overhead mean lower prices but typically means a longer fill time and possibly nothing received at all because they are at the mercy of their suppliers just as you are to them.
I prefer a retailer who has it in their possession ready to immediately it ship to me at the time I place and pay for my order. This means real time inventory, not one that is updated "regularly". How do you know when a retailers doesn't have a real time inventory? When you get a package missing items you ordered with a note saying "back ordered." What!?! When you placed the order it showed "In Stock" when in reality it was in stock as of the last inventory update which may have been more than 24 hours prior to you placing your order.