Control visibility of command button in detail section of Access Form

My form is used to display a list of items that customers purchase filtered by customer.
Form Headers are:  Customer, Qty, Price, Total.
Detail lists all purchases for Customer.

Customer      Qty      Price      Total
A                      1          $2.00     $2.00
A                      2          $1.00     $2.00
A                      3          $2.00     $6.00
A                      4                         $0.00    [Button Visible Here]

I want a command button to be visible in detail when Price is null otherwise the command button is not visible.  How can this be done?