Need Chargeback and accounting software for Unix...

[Animals]

Our site is going to start charging dollars for computer usage
so we'll need some software that takes the basic accounting statistics
and generates a list of users and how much to charge them.  We
would like to charge by CPU usage, disk paging, I/O, disk usage,
pages of paper used.... the works.

Is there any public domain software out there available to do this
or are there commercial packages that can do the job?  I know that
there are certain Universitys that DO have such a mechanism running
at their sites.