Billing based on unit price

We are using Projects Costing and Billing module. We are engineering company and we bill our client based on work performed. For e.g., Drilling/feet, no of lab test performed.  So if we have perform  5 lab test and we charge $500/test, we want to create $2500 invoice using this data. It has nothing to do with labor hours.

We want to bring this data into Oracle projects and use it for billing. How can this be achieved?

Thanks,

Anjula