The useful answer is a range, not a flat number
A short Rise-style informational module, a complex Storyline simulation, and a multilingual compliance curriculum are all “custom eLearning,” but they are not the same production problem.
Instead of estimating from a generic per-slide price, start with the business problem, audience, delivery requirements, and level of learner practice. Those variables determine the real production effort.
The main cost drivers
Common cost drivers include instructional design, SME interviews, scriptwriting, visual design, interaction design, software simulation, narration, video editing, LMS testing, accessibility review, translation, and stakeholder review rounds.
The biggest hidden cost is usually unclear source material. If the content exists only in SME knowledge, old slide decks, PDFs, policy manuals, or scattered job aids, the project needs more analysis before development starts.
How to lower risk before requesting an estimate
Gather the source materials, define the intended learner behavior, identify required compliance or reporting rules, and decide whether the course needs basic information delivery, guided practice, branching scenarios, simulations, or job-performance assessment.
A planning checklist makes this easier because it translates an internal training request into a buildable scope.
When a higher investment makes sense
A higher-development course is justified when mistakes are expensive, compliance risk is high, behavior change matters, the audience is large, or the same course will be used for multiple years.
In those cases, better interaction design, feedback, and assessment structure are not decoration. They are part of the return on the training investment.