Buy the oldest second hand version of an iPhone that supports Lidar. Doesn't matter if the screen/battery is busted. Strap it to a drone and have your custom app broadcast that data somewhere while you're flying around.

How big is your backyard anyway? Maybe you could just walk around it with a selfie stick instead.

In which case, code the app first, buy iPhone, try it out the same weekend, return for free. :)