The Product Price is set to 0.00
The Product Priced by Attributes is set to YES
The attribute prices are defined without the price prefix of +
The Display Price is made up of the lowest attribute price from each Option Name group.
If there had been a Product Price, this would have been added together to the lowest attributes price from each of the Option Name groups to make up the display price.
The price prefix of the + is not used as we are not "adding" to the display price.