Why most of the VFD inverter pressure booster pumps are so expensive?

The reasons why most of the VFD / VSD Inverter Constant Pressure Booster Pumps are expensive are as below:

VFD / VSD Inverter cost: Most of the VFD / VSD Inverter Constant Pressure Booster Pumps are equipped with general inverters which can also be used for fans, compressors, and many types of machinery. Most of the time, the parts and functions of a general inverters are not just for water pumps and might be wasted. Therefore, the cost of general inverter is too expensive for VFD / VSD Inverter Constant Pressure Booster Pump.
Other parts: It needs a 5-ways connector, a pressure tank, a pressure sensor, a pressure gauge, a control box, and a base plate to put together a standard VFD / VSD Inverter Constant Pressure Booster Pump. To purchase all those parts are quite expensive.
Labor cost: It takes a long time to put together a water pump, a VFD / VSD Inverter, a 5-ways connector, a pressure tank, a pressure sensor, a pressure gauge, a control box, and a base plate to become a VFD / VSD Inverter Constant Pressure Booster Pump. As a result, the labor cost would be also expensive.