Need advice on substituting a cheaper yarn for silk yarn

[noejusti]

I have been planning on making a sleeveless "high neck lace top" seen on page 92 of Vogue Knitting, Holiday 2005. It is made of silk yarn (category 3 of standard yarn weight system). The economical woman in me (OK, the cheap side of me) doesn't want to spend a lot of money on silk yarn. And I feel better knowing I am using a renewable source of fiber that doesn't involve killing the animal to get its fiber. Does anyone know a good substitute yarn I can use that will work as well with respect to drape and fit of the garment? Would cotton work, or a synthetic? I would appreciate any opinions, even if it is to convince me to just bite the bullet and buy silk yarn. Thank you.