This is my attempt in creating a cursor in a stored procedure
--Second Stored Procedure-- CREATE OR REPLACE PROCEDURE sp_GetDiscountedRate (DiscountCode IN
You go through all the trouble of calculating "REVISED_RESERVATION_COST", and then you don't read it from the cursor.
"REVISED_RESERVATION_COST"
No wonder Oracle is complaining. You need a variable for this column as well.
I would also advise you to learn to use modern, proper, explicit JOIN syntax.
JOIN