Can we replace an embedded system design with a general purpose computer or a smartphone?
It seems you are looking for something called a single board computer.  These things exist in many varieties and tradeoffs, and the industry is quite competitive.  You can get something beefy enough to run Windows 10 IOT, for example, for $350, including the Windows license and 0-70&deg;C operating temperature.  There are also ruggedized fanless computers in small boxes for a bit more money.

In your case, you have to look carefully at the operating temperature rating, and get something designed for a high-vibration environment.  That's basically the difference between something low end like a Raspberry Pi and a real industrial SBC.