The supplier's price is only part of the landed cost. Spread transport, insurance, handling and other attributable costs over the units you can sell.
An example with numbers
You buy 100 units for $2,000 and pay $300 for transport and $100 for handling. With nothing else, the cost is $24 per unit. If only 96 can be sold and you recover nothing for the rest, it rises to $25.
Try it with your numbers
Separate final costs from recoverable taxes and payments that only affect cash. Check duties, currency and tax treatment for the actual transaction.
This calculator is on its way. In the meantime, you can do the calculation on paper or in a spreadsheet.
Example figures for learning purposes. They are not a recommendation and do not replace professional advice.