I asked Serafina to spread the word (werd, yo) about Bangkok Thai Silks, whom you can now buy directly from (used to be via e-bay only), and their prices are pretty darn good for silk taffeta. But I neglected to mention it myself. Until now. Their same silk is going for $19.99/yd on e-bay, but there are significant discounts buying directly ($9.99-$16.99). Note that you will need a paypal account to buy from them.
This is, by the way, the vendor I used to purchase the "cobalt-green" shot silk for my elevation gown:
The silk hoarder in me would love to keep it a secret, but I love you all too much not to share.
Enjoy! (and I'm sorry)