How To Charge For Usage?

Not really sure if the is the right place to ask... But I was wondering... We have a data warehouse system setup where we host multiple DB's for differant customers. Now currently the way they are charging for the usage is like $0.005 a row for all major tables... IE not the tables we need for processing data for that customer. However we are looking at implimenting Sharepoint Services here and using this SQL Server as the backend SQL Server. Well I have been asked to see if I could come up with a better way of billing for the SQL Usage. Here are some of my thoughts and just wondering what you all do or how you feel about this:

For the Data Warehouse Part when billing by the per row instance someone with a 2 column table and 500 rows will be billed the exact same amount as a 50 column table with 500 rows but yet the 50 column entries would use more space.

Billing for hard drive space utilization could be tricky cause I would either A need to more all my staging type tables to another db for processing or make sure I wipe the staging tables out after each update.

Now I am not sure how Sharepoint works or how it saves data... but can I put each site I have under share point in their own DB? IE Client1 SP site is in the Client1 DB and Client2 SP site is in Client2 DB but both of them are running through the same Sharepoint Instance?

Would be it better to bill a flat rate in number of columns in a table and then number of rows in that table? I am not sure... Any advice you all can give would be greatly appricated.