Can’t answer your question but if he’s looking to go OOS, your best bets are going to be Alabama, Mississippi State, West Virginia, UAH, Arizona and others - if you’re looking at pure cost. Auburn wouldn’t be as cheap but maybe a more similar vibe to Clemson.
Bama tuition would be about $2K for you - $30.5K off ($28K auto merit and $2,500 for the ACT).
Not suggesting you go that way - just noting because you mentioned cheaper in-state options.
If you are looking at cost, there’s lots of “inexpensive” OOS options with strong engineering program. Mine chose Bama over Purdue (admittedly against my desire) but his outcome wise was likely just as good.
Best of luck at Clemson, your in-state, or any other school you take an interest in.