To view a list of product costs, go to Reports > Inventory KPI and view Variants.
Click on the gear icon at the top of the page to choose information to include in your report.
For this report, you want to be sure that Cost Price and is selected. (Use the 'column search' to quickly find the metric you need.)
Click the gear icon again to collapse the column options. Your report will refresh with cost price included.
Finally click on Export at the bottom of the page to create a CSV of your data.