Use contribution, not top-line sales
Every order must first repay garments, DTF transfer cost, payment fees, packaging, reprints and other truly variable costs. Only the remainder can cover new monthly overhead and recover setup capital.
Make the downside survivable
The downside case reduces order volume and increases variable cost. It still does not model a major service call, missed launch or financing interest. Add those to capital or monthly fixed cost and rerun the model.
Compare outsourcing before ownership
Buying a printer is easier to defend after outsourced transfers have proven order flow. Compare in-house contribution with outsourced contribution, then value faster turnaround and production control separately rather than treating them as guaranteed revenue.
Build the variable-cost input first
Use the DTF cost-per-print calculator and add the blank garment and any per-order fees. For machine-specific width, white-ink, warranty and service evidence, use the exact-machine comparison.