Have you tried using a cross-tab object? First you need to create a formula which breaks out the contract ranges into categories. Then do the cross-tab using the category formula as the row and use the charged amount as the column. Then you can do summaries and percentage calculations across the group based on category.

I think you're just fine using the Command object as the data source. Since you're becoming more familiar with it then you'll be able to keep writing more advanced SQL queries. The other thing to consider is that if you have access to the database, then you can create stored procedures instead. This helps consolidate all your SQL in a central location and maintenance is easier than having to track down SQL in various reports that may have been distributed out.