In my experience the biggest multiplier isn't any single variable it's the interaction between them. Fanout × retries × context growth compounds in ways that linear cost models completely miss.
The fix that worked for us: treat budget as a hard constraint, not a target. When you're approaching limit, degrade gracefully (shorter context, fewer tool calls, fallback to smaller model) rather than letting costs explode and cleaning up later.
Also worth tracking: the 90th percentile request often costs 10x the median. A handful of pathological queries can dominate your bill. Capping max tokens per request is crude but effective.
The phrase "uncontrolled human experiment" is doing interesting rhetorical work here. It frames the status quo as the experiment and regulation as the control—when historically it's been the reverse.