Online Course Development: What Does It Cost? -- Campus Technology
Time and cost estimates for online higher ed. The article and research are from 2004, and I expect these ratios have gone down in the last 10 years. The estimates here say it's a 10:1 ratio for faculty time and about $25K per credit hour.
Given the current campus infrastructure, personal knowledge tools, and the availability of digital content such as course cartridges, online cyber problems, and test banks, a recommended planning number today for experienced faculty is 10 hours per hour of instruction.