The cheapest I found was 30 for about $33 with shipping. Here is the website:
http://www.sew4less.com/product/1651/more_info
http://www.jhittlesewing.com might have them for less, but you have to sign up for their emails in order to get access to their catalog. I'm not sure their catalog has a search option either.
You could also try
http://www.shoppersrule.com . If you find the right bobbins, you can submit the price you want to pay and they will either okay it or counter. You could wait for a free shipping week to eliminate that cost too.