How can I add a custom price to a cart as an attribute of product type in Drupal Commerce?
Below these modules will help you with bit of customization or addons

Commerce Product Attributes


  This module provides some enhancements to the Drupal Commerce
  attribute handling.


Commerce Product Option


  This module allows you to add user-customizable options to the
  commerce "add to cart" form. You do this by defining "option sets", to
  which you can attach any field of your choosing. These option sets can
  then be added to your commerce products using entity reference, after
  which the fields in your option set will show up in the add to cart
  form.


Commerce Pricing Attributes


  This module provides some enhancements to the Commerce Product Option
  and Commerce Product Attributes handling by applying pricing rules to
  custom product attributes. So, you can add attributes to products that
  affect the final product price.