The heart of the RC system is its servos. These are electric motors with a gear box and a crank or such like to provide mechanical movement, which is also linked to a pot to provide electrical feedback of the movement. So if you have some one capable of building one, get him to build at least three (steering, speed, gears)!! If it is beyond your capabilities, buy a ready made servo, then you also get linked into that servos feedback system (normally PPM with a 1mS pulse). The electronics is quite easy, its the mechanical stuff that is difficult.
Frank