list generation/email address services

We are a sales consulting company that is looking for help researching lists of US companies and filling in missing contact information, especially email addresses. We would like to try your service with a small list of 100 contacts and have you fill out the email addresses in an excel spreadheet. Once we are satisfied, we will use you for larger lists on a regular basis. Please provide pricing for this project and for future projects with blocks of 250 contacts per list. Also please tell me about your methods for obtaining the email addresses. Thank you.