This is the amount that you paid per unit when purchasing your Item. The Acquisition Price is not required but is highly recommended as it can be helpful in evaluating the performance your rental collection later down the line.
If you are entering 100 of something in the Acquisition Quantity and you paid $1,000 total, you'll enter “10” in the Acquisition Price field.
If you plan to import your inventory (instead of entering it manually), make sure that this column is labeled "Acquisition Price" on your spreadsheet.
Also see the Inventory Profitability Report support article.