Solve the following sql problem:
Identify the cost difference between Priority and Express shipping methods.

Schema:
SCHEMA:
- Table: address_status
  - Column: status_id
    - Samples: [1, 2]
  - Column: address_status
    - Samples: [Active, Inactive]
- Table: author
  - Column: author_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: author_name
    - Samples: [A. Bartlett Giamatti, A. Elizabeth Delany, A. Merritt, A. Roger Merrill, A. Walton Litz]
- Table: book_language
  - Column: language_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: language_code
    - Samples: [eng, en-US, fre, spa, en-GB]
  - Column: language_name
    - Samples: [English, United States English, French, Spanish, British English]
- Table: country
  - Column: country_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: country_name
    - Samples: [Afghanistan, Netherlands Antilles, Albania, Algeria, Andorra]
- Table: address
  - Column: address_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: street_number
    - Samples: [57, 86, 292, 5618, 4]
  - Column: street_name
    - Samples: [Glacier Hill Avenue, Dottie Junction, Ramsey Avenue, Thackeray Junction, 2nd Park]
  - Column: city
    - Samples: [Torbat-e Jām, Beaumont, Cayambe, Caldas, Ngunguru]
  - Column: country_id
    - Samples: [95, 37, 60, 47, 153]
- Table: customer
  - Column: customer_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: first_name
    - Samples: [Ursola, Ruthanne, Reidar, Rich, Carline]
  - Column: last_name
    - Samples: [Purdy, Vatini, Turbitt, Kirsz, Kupis]
  - Column: email
    - Samples: [upurdy0@cdbaby.com, rvatini1@fema.gov, rturbitt2@geocities.jp, rkirsz3@jalbum.net, ckupis4@tamu.edu]
- Table: customer_address
  - Column: customer_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: address_id
    - Samples: [606, 266, 376, 655, 273]
  - Column: status_id
    - Samples: [1, 1, 1, 1, 1]
- Table: order_status
  - Column: status_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: status_value
    - Samples: [Order Received, Pending Delivery, Delivery In Progress, Delivered, Cancelled]
- Table: publisher
  - Column: publisher_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: publisher_name
    - Samples: [10/18, 1st Book Library, 1st World Library, A & C Black (Childrens books), A Harvest Book/Harcourt Inc.]
- Table: book
  - Column: book_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: title
    - Samples: [The World's First Love: Mary  Mother of God, The Illuminati, The Servant Leader, What Life Was Like in the Jewel in the Crown: British India  AD 1600-1..., Cliffs Notes on Aristophanes' Lysistrata  The Birds  The Clouds  The F... (truncated)]
  - Column: isbn13
    - Samples: [8987059752, 20049130001, 23755004321, 34406054602, 49086007763]
  - Column: language_id
    - Samples: [2, 1, 1, 1, 1]
  - Column: num_pages
    - Samples: [276, 352, 128, 168, 80]
  - Column: publication_date
    - Samples: [1996-09-01, 2004-10-04, 2003-03-11, 1999-09-01, 1983-12-29]
  - Column: publisher_id
    - Samples: [1010, 1967, 1967, 1978, 416]
- Table: book_author
  - Column: book_id
    - Samples: [10539, 8109, 2792, 6228, 1058]
  - Column: author_id
    - Samples: [1, 2, 3, 4, 5]
- Table: shipping_method
  - Column: method_id
    - Samples: [1, 2, 3, 4]
  - Column: method_name
    - Samples: [Standard, Priority, Express, International]
  - Column: cost
    - Samples: [5.9, 8.9, 11.9, 24.5]
- Table: cust_order
  - Column: order_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: order_date
    - Samples: [2021-07-14 10:47:19, 2020-08-16 17:26:41, 2021-08-19 21:43:07, 2021-12-23 19:01:08, 2022-06-15 01:15:35]
  - Column: customer_id
    - Samples: [387, 1256, 1335, 1480, 400]
  - Column: shipping_method_id
    - Samples: [4, 2, 1, 1, 1]
  - Column: dest_address_id
    - Samples: [1, 1, 1, 1, 2]
- Table: order_history
  - Column: history_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: order_id
    - Samples: [1, 2, 3, 4, 5]
  - Column: status_id
    - Samples: [1, 1, 1, 1, 1]
  - Column: status_date
    - Samples: [2021-07-14 17:04:28, 2020-08-16 20:23:19, 2021-08-20 05:34:51, 2021-12-24 01:29:55, 2022-06-15 10:04:20]
- Table: order_line
  - Column: line_id
    - Samples: [1024, 1025, 1026, 1027, 1028]
  - Column: order_id
    - Samples: [2051, 899, 4994, 7041, 9088]
  - Column: book_id
    - Samples: [10720, 10105, 6503, 10354, 4684]
  - Column: price
    - Samples: [3.19, 1.24, 14.74, 8.85, 15.55]

SELECT SUM(CASE WHEN method_name = 'Priority' THEN cost ELSE 0 END) - SUM(CASE WHEN method_name = 'Express' THEN cost ELSE 0 END) FROM shipping_method