I don't know if this advice is helpful or not, but I will offer it anyway. I have used Elann.com for substituting Rowan yarns. They often have a good cheaper alternative. I used them for an alternative to Rowan's Denim cotton yarns and found a good one for half the price per ball in the same color range. They have a section of their site that lists all of their yarns including the type of yarn and gauge/tension so that you can find a good substitute. I think they are located on the U.S./Canada border, so I am not sure how the shipping cost will work for where you live. The shipping cost might cancel out any benefit you get in the discounted yarn. But maybe it will work for you. Check it out.
Charity Projects (ongoing): "Stitches From the Heart" preemie hats and clothes