There's mountains of paper, or proprietary software used for these tests. And that's before we pay for graders and monitors(and many schools need a few extra hands to do the test according to standard due to crowding).

Getting questions on a test is actually really expensive for a standardized test. It's been a while, but I believe it cost was in the $3-4k range per question for my state's tests. These test questions go through significant amounts of review for various biases and whether they actually measure understanding/mastery of the intended knowledge standard.