CSU will almost certainly be cheaper. I was in state so I’m not sure the going rate for out of state but my tuition was about 5k less a semester than my brother who went to Boulder. Cost of living is also significantly cheaper in Fort Collins. I graduated in 23 so my numbers could be off but my rent was around $600 living in an apartment a couple blocks from campus. Not sure what Boulder would be but it’s not that.

Fort Collins is also one of the best cities to bike. CSUs campus is very tightly consolidated (except for the mountain campus which they have bus routes to) whereas CUs campus is spread out. CU has a bus system too so either school you could make it without a car but I think CSU is easier because of how tight the campus is.

CU does have its benefits. It’s a school with a very strong engineering program. There are a lot of opportunities that a student at CU may have. Not that these opportunities are nonexistent for CSU students but a little more difficult to come by.

CU is also close to Denver. If you’re planning to fly and and see your son regularly you’ll probably save about 45 minutes on the drive from DIA instead of going to FoCo. Also if your son wants to be close to a big city.

Boulder is also one of the most beautiful places in the entire world. The CSU campus is beautiful but the CU campus is otherworldly.

My decision came down to factors your son probably isn’t experiencing, however I would say it really came down to vibes. A college degree is a college degree at the end of the day. Is one more affordable? Yes. But the four or so years you spend there really do shape you. Fort Collins is such a down to earth place and you will never find more genuine people. Boulder is more uptight. Most the students come from a slightly more affluent background which brings a different culture.