You need to develop a budget with him.
at this stage, if he’s not yet decided where to go, you can use estimates based on what sort of costs his current uni of choice would be. When he gets his a level results and confirms uni, it can be done again accurately
so for ours we listed income from loan he’d qualify for based on our income and a small saving pot grandparents had gifted ( circa £2k a year). We also added into that the cost we’d “save” during term time that we’d have spent on them ( clothes, food, phone etc etc)
we then budgettted for rent ( don’t forget deposits) , food/grocery ( £50 a week 10,years ago, it costs more to feed one, and they don’t have much freezer/storage space to batch cook or bulk buy plus they need cleaning stuff too, and we did allow a little flex for takeaway/booze once per week ), phone, travel ( inc railcard) , reasonable entertainment ( we discussed and agreed to include some tickets, music, games etc) , clothes, hair cut, shoes , study materials, energy in 2nd year onwards, union fees, locker fees etc etc….
we broke it into yearly, termly and monthly income/expenses - which is key to avoid cash flow issues.
we then looked at shortfall. There was even then. Loan only just covered rent even back 10 years ago in some places.
we then agreed how much we’d contribute on top of the above income. It was beyond the max loan any student would get, even with very low income parents.
we didn’t want kids to HAVE to work during term time to pay for basics . Both did STEM courses and these leave little time for work - timetables are full, and evening workload is steep. Working during term time can really affect kids on some courses , so be mindful of that. Dh and I were both STEM grads so knew this. Deal was they worked during summer to pay for beer money, foreign travel, festivals etc and clothes etc above the budgeted amount. We expected them to work holidays and we held them to it. We used pressure like we wouldn’t put them on car insurance unless they had savings from work to pay excess if they had accident as a way of doing this.
we then said that if they wanted more money from us, they needed to show us why using budget and actual spend amounts. It taught them budgetting at young age,something both do now aged 30 plus. We all knew what was allocated for what, and agreed lifestyle choice vs cost up front.
Sounds like you could do a similar exercise now, with estimates, he is showing clear interest and the vacuum of information is producing anxiety. Some lim ate the fear of unknown and replace with a rough estimate of budget, so he can use that to influence his choices.
your dh is a numpty frankly, to imply it is unnecessary for dc to be trying to pin this down at this age