Cheapest remote mains switch

I am planning to automate as much of my home energy system as I can using Home Assistant. What is the cheapest/best remotely controllable mains switching device that will allow HA to switch devices (lights, heaters, my boiler, my immersion heater etc.)? I may need a small device that can switch on and off lights, and a larger one that can handle up to 3kW. I suppose it could be controlled by some sort of wireless system (Bluetooth, or Zigbee, or WiFi), or via the mains wiring, or by a dedicated cable.

Thank you - Rowan