In one hour chunks, per candidate:
- Engineers for the phone screens or coding assessment reviews: 1-2
- Interviewers for the on-site: 6-7. 3-4 engineers, 2-3 managers
- Reviewers for the feedback sessions: Interviewers + 0-2
This doesn't take into account the cost of HR, flights, hotels, on and on.
Giant tech companies have data going back decades now on the performance of this method vs. alternatives. The position that they blindly incur this expense for no benefits is hard to believe.
If you have a cheaper, more accurate way of identifying candidates that also improves the candidate experience it sounds like you have a winning start-up idea. Please go execute.