Questions on Extruder (delta 3d printer)

Hi LMRians!

My uncle and I are working on a 3d printer with delta mechanism! We have some questions about the extruder!

The speed (or power) of pushing the filament to the hot end? how much should it be? how it can be calculated?

We are looking for some cheap methods of extruder design! What do you recommend? because we no do not have access to any 3dprinter to use extruders on net! We have bought the hot-end of felix 3dprinter (with the stepper, thermistor and heater)