FileMaker is a relational database, not a spreadsheet program like Excel.
I suggest that you set up related tables so that you have this basic structure typical of invoicing:
Invoices::__pkInvoiceID = InvoiceData::_fkInvoiceID
Products::__pkProductID = InoviceData::_fkProductID
With this set up you can put a portal to InvoiceData on your Invoices layout. You have one record in invoices for each invoice and each item purchased, the individual rows of data in your current set up would be InvoiceData records listed in that portal. You'd access data about the product sold, such as the price by selecting the product in a drop down list or popup menu set up on _fkProductID.
Note: In many cases, the InvoiceData table is named "lineItems" I've used the names found in the Invoices starter solution that comes with recent versions of FileMaker.
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained