Congratulations to your son on all of his accomplishments! He should be very proud of his record, and it is obvious he gets a lot of support and encouragement from his family.
Because he is a National Merit Finalist, there are good schools that would be thrilled to have him attend and will pay for tuition, room, and board for him…a full ride! Getting to go to college for free is amazing (and they will frequently supplement the free education with special opportunities for research, special events, etc once the student arrives on campus). Schools that will be essentially free (you would probably need to pay for books and transportation back home). These websites can give you some ideas:
This website is not just about full rides, but will say whether there may be scholarships for tuition only or if there are scholarships that are competitive (i.e. not guaranteed), but that would be possibilities for your son: Selective Colleges Offering National Merit Scholarships
The schools on these lists would be safeties (extremely likely to be admitted and affordable).
Whatever school he attends, you want to make sure it is ABET-accredited. If he decides he wants to go into engineering, that is a requirement for most professional engineers. You can look up whether a school is ABET-accredited (and for which fields) here.
Your son is very blessed that you are willing to do anything you can to support him, including going into debt. Going into debt, however, is not necessary. As shown above, there are many schools where he can go for free. Also, having debt can impact what you can pay for yourself and any other family members, as well as impacting your retirement. Nobody will give you a loan for you to be able to retire; it is generally best to limit debt as much as possible.
If you are eligible for a Pell Grant, then you are going to also want to take a close look at schools that meet financial need (as the school defines it). Schools don’t calculate a family’s need the same way, so you will need to fill out the Net Price Calculator for each school you’re considering.
This list indicates whether a school is need-blind (whether it considers how much need a family has in deciding whether to grant a student admission) as well as how much of a family’s need is usually met: Need-Blind Colleges
With your son’s interests, I would take a close look at Harvey Mudd. It is need blind and meets the full need of its students. It’s got very strong computer science and engineering programs, but it also has liberal arts requirements so your son can continue with history and economics. It’s also part of the Claremont Consortium, so he can take classes at any of the 4 other colleges in the consortium. Run Harvey Mudd’s Net Price Calculator and see how much it would cost your family. Then think about, is that price affordable for your family? Can you pay for it without taking out any loans? Often some of the most competitive schools (for admissions) can be very affordable for families with low incomes. Take a look and let us know how things turn out.