The first home costs what the kit costs. The thousandth home costs almost nothing extra. The curve between them is the point.
The fixed costs of a kit (the UV flashlight, the bottle, the branded packaging) are paid once and amortized across every home the kit screens. The reagent cost per home (one bottle refilled) is small once you are using the gallon. So the curve drops sharply early and flattens to a long tail at the reagent floor.
A program that buys a kit for $50 and uses it for 10 homes is paying about $8.50 per home. The same kit at 500 homes, with refills, costs the program closer to $4.35 per home. Same kit. Same program. The difference is just how many homes it screened.
At enough scale, cost per test approaches the marginal cost of the reagent itself, which is pennies. A program that started at $8.50 per home in the first month ends up at about $4 per home by the time the gear has paid for itself, simply because the gear has paid for itself many times over.
Front-load the gear, then plan for cheap refills. Buying the kits is the up-front capital expense. Refilling and reusing them is the operating expense, and it is small. The right way to budget a public dust program is not as if every home is buying a new kit. It is as if you are buying a small fleet of reusable instruments plus a tank of reagent.
This is the model the interactive prevention-model lets you plug program-specific assumptions into. The curve above is the shape behind those numbers.
Numbers in the chart are illustrative of the curve's shape, anchored at the $50 public-health program rate, with the 1-gallon refill at $490. Real per-test cost depends on kit price, refill price, and how many tests the program actually runs. Adjust the prevention-model sliders for your program's specifics.
