Go to any yarn shop with your pattern and they'll be glad to help you find a substitute. Or, go to any store that sells yarn, and read the packages...look for 3 0z, 85 yards on the labels. You could then look for what you find on line.

You need to look at yarns with a 3 to 3.5 stitches per inch gauge. That is the gauge of bulky yarn. Look online at yarn sites or check out what JoAnn's and Michael's carry which will be relatively inexpensive yarn. You can sub one bulky yarn for another as long as the gauge is equivalent.