Broadly speaking, you probably want some kind of relay either mechanically switched or electronically (e.g. with MOSFETs). Most people would prefer an electronic one as they won't make a "clack" noise when turning on or off. Electronic may or may not be more expensive, it depends on the rating.

The key factor will be getting one that is rated to the voltage and current draw of the motor. If the motor is AC powered (e.g. 240V) and is rated at 1200W, then you will need a relay rated to 10A. Same thing goes for DC, just smaller numbers.

You should be able to find some kind of wireless relay on Amazon as well. There are plenty of WiFi ones I'm sure if you want to use an app. There's probably also an assortment of radio ones if you want to use a fob key. The easiest would be to look for something that is a kind o "inline adaptor" so that you plug it between the power and the motor, and it powers itself.

You can use rc kits, hobby stores will have relatively simple systems designed for custom rc cars that you can plug and play

In the same vein you can always find alert cheap rc cars at your local second hand store, goodwill has em for afew dollars and you can scavenge whatever you want

These days though I prefer an esp32 or an arduino with a Bluetooth shield, much easier to work with

IANAEE. For an on-board application you can create a simple switch with a transistor. https://www.electronics-tutorials.ws/transistor/tran_4.html

To make something wireless you'll probably want to go with a microcontroller or Raspberry Pi and hook up GPIO pins to the motor controls. A transistor wouldn't be needed in that case as the microcontroller can hold the pin high or low depending on what state you want.