I took at look at your site, trying to get a feel for your offering, audience, marketing approach, etc. While I'm certainly no expert on homeschool curriculums, I do have experience working with a small company that sells high-end training curriculums B2B. The bulk of that company's leads come right from their web site (inbound), and it is mostly organic and not paid. Every page's content (i.e. a specific course) is optimized around a very targeted and well researched set of keywords to get visitors there, and the web pages are designed with forms and offers (e.g. complimentary module to review) to turn those visitors into leads. You still have to sell, but selling is much easier when you have good leads that are by definition interested in what you are selling.

A good organic inbound strategy might be very cost effective, and can be integrated with some ads and pay per click as well. I would also bet there are some list resources for people doing/interested in homeschooling. This would allow you to integate some very focused outbound email marketing with your web presence.

Hope this helps ....