Calculate for three variables

I have a problem that seems simple at first but is confusing me. Any help will be very gratefully received.

I have the following data;

No. of parts per load
Price per part
Surface area of each part

This is to help me work out the price we should be paying for a part depending on the size of the part and the number of parts in a load.

I have already worked out averages from the data available; there are 3030 parts per load, the surface area of each part is 2146(mm˛) and the price per part is €0.6431.

I want to calculate the price if the surface area of the part is different and/or the load is different (e.g. if the surface area is 2000mm˛ and the load is 1500 pieces).

Can anyone help me with this calculation?

Many thanks
Steve R