Advice for Switching High Current Motor (Relay vs. SSR vs. Mechanical Switch)
Mechanical Contactor in my opinion will be cheaper, try getting motor starting grade 24vdc and then you can drive it with a WebRelay output (24V). I haven't used it for well pumps but assuming your motor is a DC pump with conventional features, you will als want to withstand  inrush current being high, You did not specify motor features or duty so it might be hard to size contractor with out. WebRelay also has inputs so you can use them on the aux contacts to monitor. You can power webrelay form separete 9v source, 24V or even PoE.