For some folks purchasing crochet materials isn't a financial challenge though I can't say I know many who have enough disposable income to let go of 20 or 30 dollars for a skein of yarn. At least not in person. LOL I have been told they are out there though. Out there sort of like pixies or fairies or trolls under bridges if you ask me.
For the rest of us NuMei (http://www.numei.com/index.htm) is a wonderful and reasonably priced alternative to some of those higher end yarns. I was looking for a reasonable ribbon yarn to use for a project from Doris Chan's new book, Amazing Crochet Lace when I stumbled upon this on sale at NuMei. It's called Fluid ribbon yarn and the color I chose is Italian Plum. You can find samples of the colors here: http://www.numei.com/fluid.htm
I fell for it right off and the price is so reasonable ($13.90 for 10 balls) I was able to purchase enough to make the project I had in mind at about a third (or better) of what it would have cost me at any of the other sites I had looked at and even in the stores I'd been searching in. They have a variety of yarns with prices beginning in the $8 to $10 dollar range and going up from there. Mind you, this is for packs of ten balls per pack. It's definitely making it hard for me to curb my YAS this season!
A friend of mine and her girlfriend raided the local thrift store today and she came by to show me her loot. She is picking up odds and ends for a scrap yarn afghan and today she found exactly what she needed. LOL! Bear in mind this is a friend that I hooked on crochet. I actually think it was the combination of her other friend exposing her to it (and nagging at her for years to try doing it) and me exposing her to the possibilities and endless projects she can do if she just learned to crochet. After watching her friend for years and me for a couple she succumbed. Guess they should post signs up not only at stores but at crocheters homes as well warning of the possibility of addiction by osmosis!
Another site I frequent is Smiley's yarns. They have a $40.00 minimum which isn't hard to do because the prices are so great you can't stop yourself from filling up. I cannot count the number of times I've gone there and just blown my yarn budget in a couple hours of browsing. http://www.pagelinx.com/cgi-shopper/loadpage.cgi/smileysyarns/ezshopper?user_id=8600-20070215&file=index.htm
I love this place! I've never had a problem with any of their products and their shipping is lightening fast.
For yarns, those are my two usual suspects although there are other places that I keep an eye out for great sales so I can splurge when they occur.