Yarn Substitutions?

Hello there... can I ask your advice? Mom suggested I put some sweater yarn on my Birthday wishlist. (Yeah, so it won't get here by my birthday... that's fine with me. Anyway, it's my fault for taking so long to get around to it.) Since I now have yarn for my Canada sweater, I'm looking at yarn options for Williamsro and Rocktorp from CTH Noro Book 2:

Eep! Have you seen what Cash Iroha costs!?! (At regular prices, yarn for Williamsro costs over $200 US!) And Rocktorp also calls for Noro Shinano, which is discontinued. (Available on ebay, but I'd like my mom to be able to get all the yarn from one source, if possible, and I'm also not sure how she feels about ebay.) So I have two questions:
1. What is a good replacement for Noro Cash Iroha (it's held doubled in Williamsro, and single in Rocktorp) that's significantly cheaper? Given the high silk content, I'm not sure what will have the same drape and sheen.
2. What's a good replacement for Noro Shinano? Is Noro Silk Garden similar?

I think I'll go hunt down yarn for Kepler... that should be easier. In fact, I have a bit of leftover in my stash that might be an appropriate yarn... I need to swatch it to see how it works.