They are also a FIRE risk i they get to hot. PUT a fuse in line with it. Power wasted = heat!!!
Big enough ones run reasonably cool. It is only the very small ones (i.e. 2.5W vitreous enamel) being run at their maximum rating that get hot enough to affect their surroundings, and that takes time. Big ones like the 5/7/10W ceramic blocks have more surface area and stabilize at a much lower temperature. Once the required value is known, that value inly needs to be bought once. Crane motors are not likely to be permanently running, so the current limiting resistor does not get time to over-heat, and has plenty of time to cool down. A length of heating element being run at considerably less than its designed current will not get that hot anyway. Certainly not as hot as the base current resistors in the venerable Hitec Gold Brick ESCs.
Like I said, the inefficiency is not likely to have a noticable effect on run time, cranes have a very thin duty cycle.
One alternative is to use motors recovered from servos. Already the right voltage for running off the radio supply, but they do need a "proper" ESC with a deadband so that they can be stopped.
Almost any ESC that uses a relay for reverse is going to control a motor powered by a low voltage, like the ones mentioned by chas and John W E. The Mr RC World one has a built in soft start/stop which can make things tricky when working a winch. Overshooting when trying to stop is a PITA.