Letting the user set the price

{ "rules_user_price" : {
    "LABEL" : "User Price",
    "PLUGIN" : "reaction rule",
    "REQUIRES" : [ "rules", "commerce_line_item", "commerce_product_reference" ],
    "ON" : [ "commerce_product_calculate_sell_price" ],
    "IF" : [
      { "entity_has_field" : { "entity" : [ "commerce-line-item" ], "field" : "field_user_price" } }
    ],
    "DO" : [
      { "variable_add" : {
          "USING" : {
            "type" : "decimal",
            "value" : [ "commerce-line-item:field-user-price:amount-decimal" ]
          },
          "PROVIDE" : { "variable_added" : { "variable_added" : "Added variable" } }
        }
      },
      { "data_calc" : {
          "USING" : { "input_1" : [ "variable-added" ], "op" : "*", "input_2" : "100" },
          "PROVIDE" : { "result" : { "result" : "Calculation result" } }
        }
      },
      { "commerce_line_item_unit_price_amount" : {
          "commerce_line_item" : [ "commerce_line_item" ],
          "amount" : [ "result" ],
          "component_name" : "base_price",
          "round_mode" : "1"
        }
      }
    ]
  }
}