Relation between subscription fees and adminstrative costs
This will vary wildly by journal, and may be extremely difficult to even meaningfully define, given that many journals are "bundled" together in confidential and institution-specific contracts.  What is clear, however, is that:


Large for-profit publishers are very concerned with keeping their de facto subscription costs difficult to determine, and have quite high profit margins, and
The potential profit from open access subscription fees has drawn large numbers of predatory publishers to the field, and
Society publishers are often able to sustain journal publications with quite minimal costs, especially online-only journals.


You may draw your own conclusions from this: my conclusion is that a lot of money is made from subscription fees.