The cheapest option on paper is not always the right one
Comparing internal cost against an external quote looks like a simple math problem, but the real decision involves at least two factors a raw price comparison misses: what else your printer could be doing with that time (capacity opportunity cost), and how confident you actually are that your internal process will produce a good result on the first try (quality risk). A cheaper internal option that displaces higher-priority work, or that carries real risk of a failed first attempt, is not automatically the better choice.
How the decision works
The raw cost and lead-time comparison sets a baseline. If internal capacity is currently constrained, the decision shifts toward buying externally regardless of the cost comparison, since internal capacity used here is capacity not available for other work. If internal quality risk is rated high, the decision also shifts toward buying externally, since a predictable outside result is worth paying for when your own process is genuinely uncertain for this specific job.
Worked example
$12 internal versus $18 external, 2-day internal versus 5-day external lead time, capacity not constrained, low quality risk: the tool recommends making internally, since it wins on both cost and lead time with no capacity or quality flag against it, with buying externally shown as the alternative if a busy period later makes capacity relief worth the extra cost.
A common mistake
A frequent error is comparing only the sticker price of an external quote against your own material and rough time estimate, without ever pricing in your own labor at a real hourly rate. An internal job that "only costs materials" on paper often is not actually cheaper once your time is valued the same way you would value it for a paying customer.
Limitations
This compares stated internal cost, lead time, quality risk, capacity, and an external quote qualitatively; it does not know your actual queue state or the external supplier's real reliability. Treat it as a starting comparison, not a final decision without checking current conditions.