Costs and production requirements for developing "mainline," as distinguished from "adjunct" computer-assisted instruction (CAI), are discussed. "Mainline" programs are complete systems which teach an entire course, while "adjunct" programs supplement a regular course. Mainline CAI programs are expensive. A course equivalent to a three-credit semester course usually takes a year to write and another year to evaluate. Present costs range from at least $5,000 to $10,000 per student hour, and at best, they might be reduced to $3,000 an hour assuming the existence of languages, systems, and authoring techniques which are still under development. However, one possible individualized instruction environment which could accommodate the logistics of CAI is described and illustrated. It makes extensive use of program design and supplementary help by teaching assistants. This model, which uses as an example a course in college freshman mathematics, has been shown to be reasonably effective and to be more economical than traditional instruction. (JK)