Inexpensive silk bridesmaid dresses?

I'm not really a traditional bride. I'm going to be 40, for one thing, and my friends are all rather over the bridesmaid thing. I'm sure they'd do it if I asked, but I'm not going to and give them a break. My sister's going to be MoH, though, because it's important to me that she stands up with me on the day and is my witness on the license. However, I have several nieces at an age who would enjoy it, so I'm having four junior bridesmaids and a flower girl. The junior bridesmaids run from 15 to 10. I can't use any of the standard jr bridesmaid dress makers because the eleven-year-old is tall and very slim, and the ten-year-old is also tall and overweight. After a lot of googling, I found Pegeen.com, who have very pretty silk dresses for girls available in a zillion colors, and also do custom sizing, so I know the dresses will fit both the slim and the overweight girl. I'm getting the junior bridesmaids navy dupioni silk dresses with yellow sashes and the flower girl a yellow dress with a navy sash. My problem is my fifteen-year-old goddaughter. She's definitely a junior size and can't wear a Pegeen dress. Watters makes bridesmaid dresses in navy dupioni silk, but they're a little pricey. I don't want to force my best friend to buy a $180 dress for her daughter to wear in my wedding. Does anyone know of a bridesmaid dress maker who uses silk but is more in the $120 range? Or, artificial silk? Taffeta, maybe? I don't think satin will look good--the cheaper Watters line, WToo, does have navy (they call it indigo) satin dresses and they're more my price range. I just don't know how a satin dress would look with the dupioni silk dresses. And organza, all those light fabrics, would look terrible, I think. Maybe a poly taffeta dress? Anyone have a suggestion? It also can't be anything too sexy, this is for a young teen.

I hope the images work--one is of the Pegeen dress. That's actually a purple dress with a white sash, not navy and buttercreme, but it's close. The jr bridesmaids will have a more narrow sash and a scooped neck. The flower girl dress will look like that though, just in yellow. And the other is a Watters dress I like that can be done all in navy, just to show you what I was looking at. I can get that from NetBride for about $170, which is $50 or $60 more than I'd like.

Thanks for any help you can give. I hope this isn't too confusing!

OK, the images aren't working, so here's links:

http://www.houseofbrides.com/product.php?productid=8237&cat=486&page=10

http://www.pegeen.com/Pages/TRY-IT-ON-PAGES/398-399.html