Know-How Exchange : Strategy

I am a Marketing Department of one here at a non-profit organization that provides disability services to employers and employees. Specifically, we provide disability training, support and information services to our membership organization (which includes many Fortune 500 companies). We also help our members with accessibility issues and provide a National Resume Database of educated and trained people with disabilities.

We are looking to increase our membership and we have determined that our target audience should be the CEO's of medium to large-sized businesses. We have previously marketed to HR professionals at these companies. However, we have found that the decision to make an effort to hire people with disabilities usually comes from the top. By the way, membership starts at $2,500 (so it is not cheap).

So my question is...With the limited marketing budget afforded to our non-profit organization, what is the best way to market and sell our memberships? If we were to advertise, what media outlets would allow us to reach our target (CEO's) without paying through the nose? Finally, we hold an annual conference to attract potential members, does anyone have insight into marketing a conference?

Thank you all for your help.