Some things are so much cheaper there that it pays to stock up. Many times, I can get 20 rotary cutter blades - 45mm - for less than the price of five, and delivered to my door. I also buy used quilting magazines, when the price (with shipping included) is less than a dollar an issue, sometimes as low as a quarter apiece.
You can set up searches to let you know when something you are after is listed at your price. Read the descriptions carefully, and be sure to ask any questions up front.