USC with the half tuition ride that may come with NMF status, is still very expensive, note cost of attendance is now $77,459 a year. I think National Merit only gives one a break on tuition, not the fees, room or board.
https://financialaid.usc.edu/undergraduates/prospective/how-much-wil-my-education-cost.html
National Merit really is not as good as it seems, especially for a CS major, but it will help at Case Western, to get very top merit, if you put Case Western as his top choice. Thats the other problem with National Merit, he has to pick ONE school and only one as his top choice, so it usually leads to zero dollars for a CS major.
. GaTech full price, and Case with their good 2/3 tuition merit are usually cheaper than UCS with the 50% off tuition merit. The only really good National Merit Finalist deal for a CS major might be Arizona State Barrett Honors College. Arizona State will fly your child to Tempe/Phoenix, actually send air plane tickets in a letter explaining the program. I do think Arizona State is a good education. And it will be close to free, as I remember, they love National Merit Scholars.
All the other NMF deals, like UT Dallas, U of Oklahoma, and , U of Alabama, may be ranked lower than your son wants for CS, compared especially to U of Wisconsin or U of Toronto, where you have a good price.
We could not find a National Merit deal that fit our sons criteria for CS program, except Arizona State, but son did not want that large of a school. I do think being a finalist will help get into some well ranked CS programs though, so its still helpful.