If you're planning on making a purchase online, make sure to check for discounts and coupons first. You can do this at Retail Me Not.
If that doesn't work, Google the name of the retailer and something like "promotion code" or "coupon."
Today I made a purchase at The Teaching Company and used a code found at Retail Me Not (CVSC) to get another $20 off of the sales items I purchased. The courses I bought were already 70% off. The shipping and handling was $20, so it was like getting s/h free in addition to a huge discount.
BTW -- If you are interested in The Teaching Company's courses, each and every title goes on sale at least once a year for 70% off. If there is a course I would like to purchase for my homeschool then I wait patiently for it to go on sale. Other options for The Teaching Company? EBay, your public library, and Netflix.