How to calculate cost and payload for built-in aircraft add-ons?

[MinagawaRailway]

I am a 3DCG aircraft add-on creator.

I am not sure how to calculate the cost of creating an aircraft add-on for pak128.

Is there any cost calculation sheet available for aircraft?

Also, regarding the pak128 built-in aircraft add-on, the payload seems to be very different from the actual payload of the aircraft.

Is there a unique calculation method for this as well?

(DeepL translation is used.)