Put a range on it

You rarely have perfect information at the beginning. Use the records available, direct observation, and estimates from the people doing the job to put a defensible range around the consequence. Label the assumptions so someone else can follow your reasoning.

If the annual cost might be between $40,000 and $120,000, write that range and explain where it came from. The midpoint doesn't become a fact because it's easier to put on a slide.

This helps you judge the size of the opportunity. It can keep a small inconvenience from becoming a strategic program and put a sensible upper boundary on what a solution could cost. If the range is too uncertain to support a decision, measuring the current work may be the next useful step.