So...many moms out there are into CDs for the money savings. Here's the thing no one realizes...they're ridiculously addictive. :) Many moms end up not saving a penny because they keep buying and buying cute diapers that they "must have."
As with any "hobby" it's best to go in with a plan. You can decide to go the cost effective route from the get go:
1) Use a trial/sampler package. This will help you to determine what kind of diaper you like best. Here are a few links to some online stores with trial programs:
2) Buy cheap diapers...for newborns (and up if you're braver than I) go the prefold/flats and covers route. This is the most economical form of diapering for sure.
Fitteds are nice but depending on the brand won't always save you money. For a good deal on fitted diapers try the package of 12 by Little Lions for $99.
If you are more of a pocket OS person then try: Kawaii's, Sunbabys', Nubunz, or Tweedle Bugs
3) Buy used. You can buy many of the brands you love on swap boards (there's one on BabyCenter), eBay, and even Craigs List, Diaper Swappers, Spots Corner on Hyena Cart. But, beware...you may not get what you paid for. Make sure there are a lot of pictures of what you're purchasing and ask questions! Also be willing to negotiate.
4) If you're like me and you like to try a bunch of different brands without losing too much money then you need to be willing to sell diapers you have. I never buy a new diaper for my son without selling something out of his stash first. It's true! It's my rule. And although I don't always make back all of the money on a diaper, it's more cost effective than just buying diaper after diaper after diaper.
5) Start a PIF box with friends (PIF = Pay it Forward). Throw a diaper in a box, send it to the next person on the list. They get that diaper and throw in their own, and send it on. Continue through the list until the box ends up back to you. :)
CDing can be cost effective, but it can get out of hand quickly if you're not careful. Set some parameters for yourself...discuss them with your spouse or significant other...and then follow through on your plan. :)