There are actually two reports which may work for you which are in the Contracts application.  The first is the Contract Schedule of Work In Progress.  This report is available in the Contracts application under Reports/Work In Progress/Contract Schedule of WIP.  This report will show you the Costs and Billed amounts for your contract, it will also include other columns such as estimate, earned profit etc.   A report which will show the contract item detail would be the Contract Item Billing Summary report.  This report is available in Contracts under the menu Reports/Billing Summary/Contract Item Billing Summary.  This report will not include the costs column on it.  There are a few reports in JC which will include Costs and Contract amounts.  

I hope this helps!