in the add to cart button, you have the Price, Article, version and size column set to get their values from the rspricelookup recordset.
the rspricelookup recordset relies on values from the SelectSize and SelectVersion form elements.
You would need to create another recordset that will return the correct price for items that do not have a size or version option and edit the add to cart code to use this recordset value instead.
$ATC_itemPrice = floatval(($row_rspricelookup['price']!=""?$row_rspricelookup['price']:$row_rspriceNoSize['price']);// column binding