The total cost of the textbooks is the number of textbooks multiplied by the price per textbook.
Since the number of textbooks is 99, which is an odd number, the last digit of the total cost must be odd.
We know that the last digit is either 1, 3, 5, 7, or 9.
We also know that the first digit is either 8, 9, or 1.
Since the first digit is 8 or 9, the total cost must be greater than or equal to 8000.
If the last digit is 1, then the total cost must be greater than or equal to 8001.
However, if the last digit is 9, then the total cost must be less than or equal to 8999.
Therefore, the last digit of the total cost must be 3, 5, or 7.
If the last digit is 3, then the total cost must be greater than or equal to 8003.
However, if the last digit is 7, then the total cost must be less than or equal to 8997.
Therefore, the last digit of the total cost must be 5.
If the last digit is 5, then the total cost must be greater than or equal to 8005.
However, if the first digit is 9, then the total cost must be less than or equal to 9995.
Therefore, the first digit of the total cost must be 8.
Therefore, the missing digits are 8 and 5.
The total cost of the textbooks is 8482.75.