How can I add an inventory part in British Pound Sterling as the cost of goods and have the sale price in US Dollars

You need to have the inventory management app to manage the cost in multi currency amounts.

I can share some details about how multi-currency works in QuickBooks Online, ministeam.

In QuickBooks Online, it is essential to note that there isn't a direct option for specifying a particular currency when creating an item. The system defaults to the home currency, which is the currency of the country where the business is located. 

I agree with @SIAB's suggestion to explore alternative inventory management applications that offer the functionality to handle the cost in multi-currency amounts. You can check our QuickBooks App Store and type a keyword in the search box. 

You can also access the Apps menu directly from your QuickBooks Online account by following these steps:

1. On the left panel, click Apps.
2. Go to the Find Apps tab.
3. Use the search bar to look for an app.

Additionally, check out this article to learn how to use the Multi-currency feature to do business and deal with exchange rates and foreign currencies: Set up and use Multicurrency in QuickBooks Online.

I'm here to help if you have more questions or additional concerns regarding currency management in QuickBooks. Feel free to reach out, and I'll be glad to assist you again. Have a great day!