Judith Boettcher in a Syllabus article on Online Course Development: What Does It Cost?, provides some rules of thumb

1. A Learning Management System Reduces Costs for Design, Development, and Delivery--Use an LMS
2. The More Hours of Instruction to be Designed and Developed the Higher the Cost of Design and Development
3. Design and Development of Online Degree Programs Can Coast Up to $25,000 Per Credit Hour
4. Instructional Costs Shift with Tehcnology Developments and Models of Instruction

...via elearningpost