breaking a throttle servo is pretty hard. it's usually the steering servo that gets it. i broke my throttle servo once. the screws holding the servo mount were loose and the vibrations snapped the plastic mounts.
when it comes to picking a servo, you've got a lot to choose from. metal gear servos are better than plastic geared ones. the higher the torque a servo has the more muscle it has when doing it's job. those servos are great for steering large vehicles like monster trucks and racing buggies.
they range in price from $10-$15 all the way up to $100+
good luck,
Rob