Even legal spending is necessary (perhaps not sufficient) to have an elite football program. I know UGA was criticized 10-20 years ago for having deficient facilities, no indoor practice, not a great weight room, etc. So, they spent hobs of money, legally, on that. You pretty much also need a nicer large stadium to be elite, probably the smallest venue for a near elite program is ... Oregon?
So, yes indeed, it takes gobs of money to build a near elite program today. The NIL thing has probably doubled it.