Assuming that the audit information would be used in a ~60-day period and it's being used ad hoc instead of periodic reports, Knowledesync is the lowest cost way to address this. Setup events triggering on different changes to send email notices to Administrator. Use email rules to sort and filter them automatically into appropriate folders. the information is now readily accessible to research, and very easy to modify as you go.
Writing audit logs is straightforward, but hard to maintain. Customers tend to completely ignore them until an emergency, when they discover it screwed up 3 weeks earlier ...