There was a formula in one of the sub forums that approximated chargable ticket prices quite well I forget where it was located but the gist of it was that it was a reflection of your club supporters, manager level and stadium, as well as your opponents star level.
I'm not exactly sure but I think it was Total supporters/ level attendance cap = ideal ticket price vs other 5* teams.
Winning cup games drastically improves your supporter base. You can check it in the old version. Don't forget club shops and parking lots as not having those will cripple your attendance.
I'm charging 45 per league match and 55 for CL and maxing attendance with a 260k stadium at lvl 19. My last friendly I charged 15 and had 216k/260k vs a team 1 league lower. Just adjust until you find the 4% attendance bonus sweet spot where you max profits and wait until that 4% turns to 5% consistently and then adjust the price. Just keep upgrading facilities and eventually money won't become an issue. It's finding quality players at high levels that is the hard part.