The secret to Monterey car week events is to buy all of your tickets as soon as they become offered. You can get the "best price offered" then, and only then.
The secret to the best lodging prices is to reserve your room years in advance. Living only an hour away I did that for years as it saved me two hours of driving each day. But as prices went up I am back to commuting. And sleeping in my own bed ain't bad either! Now many out of the bay area folks just take a hotel over an hour away to save $$$.
As CI allows two people entrance with each registered car, the cheapest way to get in is to register your car as early as possible. Just remember you actually need to bring your car to use this ticket option.
And now for the super secret way to get it.
Stand at the entrance and if you see a car with only the driver ask them if you (or your son) can sit in the empty seat.
Be there early! Did I say EARLY? I hear the hitch hiking/shoulder tapping line can be very long! And bring cash as the guy you pick may need a wee bit of financial encouragement.
In reality, if you have never been to CI, or Monterey car week, just bend over and spend the money. In the end you will be glad you did. You can also join one of the local car clubs. Many of them put on a week of "frugal" events for their members that will allow you to see cars all week long.
I used to attend the Pebble Beach show on Sunday as either press, or a judge. That has changed as they have really tightened up on press passes in the last 20 years. Now I watch the live broadcast from the Pebble web site. I get to see most of the class and special award winners. I do miss walking the rows of show cars. But for free I can't complain.