havban

Adding item cost field to general tab in product editing, and add stats for profit calculation.
To make the profit statistic works, you need to:
<ul>
<li>Update item cost value in each product editing page, the profit calculation will be calculated automatically for 
previous orders that includes currently edited product</li>
<li>All update to item cost post initial update, will not recalculate previous orders profit</li>
<li>If you need to update all orders related to the product disregard its purchase date, you need to set the item cost field 
empty, save it, then enter again the new item cost price</li>
</ul>

Woocommerce Ksini.com Item Cost

Adding item cost field to general tab in product editing, and add stats for profit calculation

Softedge

Products Purchase Price plug-in for WooCommerce let you insert the buying-in price of your products.

Products Purchase Price for WooCommerce

Free version of Purchase Price plug-in for WooCommerce.

Woocommerce Ksini.com Item Cost vs Products Purchase Price for WooCommerce