For a project, we often pre-calculate all needed materials and hours. 

Based on this calculation we make the quotation to the customer. The quotation only consists of the totals and not the underlying calculation details. After we get the order of the project, we want to use the quotation as a base reference.

We invoice based on a fixed price. Mostly in percentages of the whole quotation (this can be done in standard OpenERP)

So we want to see the pre-calculation of the project, compared with the real costs of the project. The comparison is viewed on totals, but we must be able to zoom in on the details. 

Can someone advise how I can set this up, or if I need custom development for this? Or maybe some custom modules are already there? How do others do this, via Budget?