Assign production value to activities

Hello

I work in a medium size company, our main business is roadway construction, and subcontracting civil works in oil & gas project.

My question is how to assign production value (in term of money) to activities,
My job is
- To make a report about expected monthly production and costs of the project.
- Updating actual costs and production each month and comparing them to planned value

We use P3 3.1, I know it is not really a project cost control in tern of accounting,
the tip we use is to assign the price value of the activity as a monetary budget with a specific account,
but the downside is as we calculate the percent competing of the project, we prefer to use cost as the weight factor( in our case is more accurate then duration and resources) but total cost is the sum of resource cost and the value price which is of course not accurate.

I hope my question is clear as my fluency in English is rather poor.
Thanks