Thanks guys now I've just HAD to make calculations... so let's see the math
$1.26 + $1.06 (50% robusta blend) = $2.32/2 = $1.16/lb x 2.2 = $2.552/kg greens
Assuming *20% weight loss = $2.552 x 1.25 = $3.19 greens needed per 1kg roasted
@ 1GBP = $0.55, $3.19 = GBP 1.76
GBP 3.15 - GBP 1.76 = GBP 1.39 left before costs
* does not include losses incurred when the roastery phone rings and the roaster get distracted on the phone while a batch is in the roaster subsequently making it fit for wholesale customers like UpChucks. For an example of such travesties, see here