Charge out rates

[Grant Collins]

This is a little off the track of comp.unix.questions but I'll give it
a try anyway..  Can anybody give me an idea of what sort of charge out
rates to apply to external users using your machine on a commercial basis?
We are an academic department with a network of Sun's with an outside interest
wanting to use them, but I have no idea what sort of rate to apply.  On
what basis would people charge?  Total connect time?  cpu time?  disk
utilisation?
Any ideas/help would be much appreciated.
Regards,
Grant.