Purchase price

QBO keeps inventory using the FIFO method.  First in First Out, that means each purchase is unique.  So yes each purchase has its own cost, but that is not shown to the user.  The cost you see on the item screen is just a reference of a purchase price.

Yes, it will affect if you select the Yes or No option when turning on the inventory feature in QuickBooks Desktop.

Follow this steps to change the price of my inventory in QuickBooks.

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We can turn on the Price rules feature for you to control the price of your products and services. We also offer discounts or charge different rates by item and offer them to only certain customers for a specified amount of time.

When creating an invoice, the price rule will automatically be applied as you add items. You can also override the price rule by selecting the rate and seeing all active price rules. Here's how to turn on the feature:

1. Go to the Gear icon on the top menu.
2. Select Account and Settings or Company Settings.
3. Click the Sales tab.
4. In the Products and services section, tap Edit.
5. Hit the Turn on price rules Beta checkmark.
6. Press Save and then Done.

Then proceed to Step 2 of this article to finish the process: Set price rules in QuickBooks Online. For available reports that will help you see the product cost, the product on hand, and more, check out this article: Use reports to see your sales and inventory status. 

To give more information about managing inventory in QuickBooks Online (QBO), check out this article: Inventory management.

Would like some assistance recording other transactions in QBO? Let me know the details and I'll gladly lay down the solutions. Also, if you have other concerns, let me hear you out. Have a great day ahead.