It would be nice to have a complete inventory management solution where we could add stock and calculate the actual buying price from supplier invoices.
We developed for ourselves a google sheet where we add all the products from the supplier invoice, all the purchased quantities, shipping costs, exchange rate conversion (with manual or automatic exchange rate), customs duties, additional fees. The script takes all the costs (except the products purchase price) and recalculates these costs into the unit price to have the final buying price including all costs.
The above price calculation could be done when adding inventory or when doing a supplier order. This clean purchase price could be save for particular batch/order of products. Later, when adding another inventory, system could show the last clean purchase price.
This is a bit complex feature like in accounting software or ERP solutions but I think a lot of customers could find this handy (integrated, all products on one place; no need to sync). Especially in Europe where you have a lot of different currencies, different accounting/inventory softwares; custom duties (most of the countries import goods) and other costs.