Budget for feature discovery and adoption
When developing a budget for implementation of a new AMS, one recommendation I always make to my clients is to budget for things staff will discover they want to do once they've learned how to use the new system.
In a nutshell, once staff has started using the new AMS and discover all the new functionality that it brings, they'll want to start using that functionality. Using the new functionality may require training and/or vendor support, so budgeting for this is important. (The vendors are aware of this. For example, Salesforce training calls this "feature discovery and adoption.")
Although on the surface this looks like just one more item for the expense column, feature discovery and adoption is actually a really good thing. What it means is the staff is using the system! And they are trying to get the system to do even more work for them.
As I've written before, user adoption is key to long-term data management success. Feature discovery and adoption is a great illustration of user adoption and one that should be strongly encouraged. So be sure to budget for it.