If you're building your own experimental aircraft, plan to spend one third to one half of your budget on the engine, sometimes called the power plant. The exact cost depends on how much of a mechanic and a machinist you are. You can buy ready-to-install power plants designed specifically for experimental aircraft or you can modify smaller automotive and snowmobile engines to power your plane.
Propellers need to be matched to the select aircraft design and engine. We'll take a look at props after a discussion of aircraft engines.