Not exactly cheap, but a bit of a discount . . . Right now A Toy Garden has a set on sale for $9.95. Unfortunately, it's just earthtones - 6 sheets sized 8X10. You can find discount codes on Sara's Toy Box blog for many of the sites that carry wool felt. So, yesterday, I got an additional 8% off of this. Finally, A Child's Dream Come True is offering a 10% discount code in the current issue of Living Crafts. Their 18" sheets run about $2.00 more than those on Magic Cabin's website. There is also Etsy to try to find some decent priced 100% wool felt. And Nova Natural has a 10 pack for $24.00. I haven't come across any coupon codes for them.
ETA: Since you're also interested in wool/rayon, check out weefolkart.com. They have a link through to a site whose name I can't remember where they are offering 20% off your first purchase. They have lots of color themed packages.
Lastly, you can always hit the thrift stores and find wool sweaters to felt. I hear they are $1.00 and less in some places. Not my neck of the woods, however. I found 5 this weekend for $15.00. And two of them were 1/2 off! But, I found merino, cashmere, lambswool and angora. The colors are melon/salmon, navy blue, charcoal grey, pink and red. 1 was a men's large 100% cashmere sweater. I'll be able to do quite a bit with that one alone thanks to its size.
