There are some crochet patterns for rugs here. I didn't look to see if any are felted. But the concept would be the same with knitting - use a larger hook then the yarn calls for so the stitches are big and loose, and crochet it larger then you want the end result to be.
You'd probably get the best deals on wool at places like JoAnns/AC Moore/Micheals where you can use 40%/50% off coupons. This week I've seen some 20% entire order coupons. You want to make sure you get 100% wool. Lion Brand fishermans wool comes in a pretty big ball for the money; limited colors, though.