Coming from Nevada, definitely look at your WUE options!
Humboldt State just became Cal Poly Humboldt, and will be expanding its STEM offerings over the next few years: Academic Programming Build Out | Cal Poly Humboldt Your son sounds like he would like the environment in Arcata. They have wonderful themed residential learning communities that can give the experience more of a smaller-school feel. (Cal Poly Pomona is a WUE school too, but it’s much more of suburban-LA commuter campus.)
Western Washington U is another one that’s competitive for WUE $ but could be a possibility. The range of STEM majors is a bit limited but the ones they have are very good.
The more rural flagships like Montana and Wyoming also offer great deals; also the Honors College at U of Arizona - not WUE but gives great merit. SD Mines offers a great, hands-on approach in a smaller school with a rural setting and a bargain price; the one downside is a high attrition rate, presumably because it’s a high-rigor program that’s easy to get into. And it may not be strong enough on the non-STEM side for your son’s range of interests.