There are very few Senior Admin I (could count them on one hand I expect). There is no Head of College salary per se - like VPs, these are full professor salary plus a meagre extra allowance (10% I think) - worth SFA after 60+% deductions and in no way reflective of the work required compared to 'just' a prof. In all / almost all cases these people will have been full prof anyway. Senior Admin II scale is the same as full prof - not many of these around either (single digits I think) - there are FAR more full profs getting that coin, some of these work hard, others don't do a tap. There are no admin staff on €250k except *maybe* head of finance, HR and legal - and even they may not be. Those III and IV scales - €110/120k is frankly not massive money these days and most of those will be busy, busy jobs.
III and IV aren't massive but still nice money. But Senior II is 170K and Senior I is well north of 200K. And as I understand it there are four Heads of College.