Hi, @riviere - sorry for all the acronyms
My daughter did not end up at Cal Poly, and she has veered away from CS into a more architecture-related major, so I’m afraid I don’t have too many relevant post-admission experiences to relate.
WUE = Western Undergraduate Exchange, which offers discounted tuition for some out-of-state public U’s among the participating Western states - so, for example, your son could attend U of New Mexico and pay tuition that’s 150% of in-state tuition, but much less than full out-of-state. You can search participating institutions here: https://wuesavingsfinder.wiche.edu/
CogSci = Cognitive Science, which is an interdisciplinary major that blends psychology, linguistics, neurscience, computer science, philosophy, design… emphases vary depending on the school and program and track-within-the-program. At UCSD, CogSci is one of the non-Jacobs majors that a fair number of kids who could not get into CS choose in order to still study a lot of CS within CogSci. (Although of course there are also plenty of students for whom CogSci is their first choice major.) There’s also a Math+CS major outside of Jacobs, but that’s an impacted major also. There is no straight-CS major at UCSD other than the one in the engineering school. (UCLA is a little like this too - there’s CS in engineering, and there’s Linguistics+CS that is not an engineering major, but no non-engineering straight-CS.) Other UC’s do have non-engineering CS majors - Berkeley and Davis for example.
ELC = the program that guarantees the top 9% of graduating HS students in CA admission to a UC campus, although not necessarily the one of their choice. If an ELC student is shut out of the campuses they apply to, they’ll receive an offer from Merced. http://admission.universityofcalifornia.edu/freshman/california-residents/local-path/index.html
You don’t have to do the full-blown FAFSA to get an idea of your EFC (expected family contribution). Pick any random university with great financial aid - let’s say Stanford for example - and run their Net Price Calculator: https://financialaid.stanford.edu/undergrad/how/calculator/ If you don’t qualify for need-based aid there, you won’t anywhere - Stanford’s aid is the best case scenario. If your EFC at Stanford is 35K or less, then need-based aid may be part of the picture for your son at some schools; if it’s higher, then you’re probably looking at finding schools where your full-pay cost is within your budget, or where he can get enough merit aid to get to your price point.
As to UW-Seattle, direct-admit to the CS major is very very competitive, even for WA residents, and they give heavy preference for direct-admit to in-state students. So the odds of a CA resident getting direct admit to CS at UDub without sky-high test scores and a near-perfect unweighted GPA are very low. Also, the max merit aid at UDub won’t get the price down to $35K/year or below, anyway.
You might want to have your son try the ACT. He seems like he’ll do well on the math side on any test; and he might turn out to be one who has more of a knack for the verbal parts of the ACT than the SAT. (Also the ACT has the science section that he might do very well on.)
Sorry for all the daunting info about how competitive it is for CS; but your son should have really good prospects - it’s just better to know up-front how tough it is at the ultra-competitive schools. There are plenty of excellent programs that he’s well-qualified for - you just have to find the right combination of fit, competitiveness, and cost.