I posted the first part of the article on SQL Server Chargeback strategies over on InformIT: http://www.informit.com/guides/content.aspx?g=sqlserver&seqNum=311
The big point to make is that you will have to develop this system yourself, since there is no way a vendor can decide how much you should charge, or even what you should charge for. The best they can do is to instrument their technology to help you track the resources your users are taking. In this article I cover the things you should decide on to develop your cost models.
Next week on Friday I'll post the second part of the article, which has sample cost models and some code you can use for the process.