Michel Platini wanted the Champions League final to be moved to Saturday so that more children could attend. The cheapest ticket for this year's game at Wembley is £150 plus a £26 "administration fee". So that's just for the children of Barclays bank executives, Russian oligarchs and deposed Middle Eastern autocrats, then.
I think that price is for the cheapest ticket in a neutral seat. Not sure why there should be "neutral" seats in a European Cup final but if they are selling them they should charge a bomb to subsidise cheaper tickets for proper supporters.
European teams generally have a poor away following compared to the big English and Scottish clubs (I think Milan had less than 10k in Istanbul, Liverpool more like 40) and so if the final is between 2 non English clubs then I would think it will be 80% corporate with a small contingent of actual fans.