High torque motors are practically just a regular, internally commutated brushless DC Motors mounted with extra gear mechanism at the top, to either increase the torque or to reduce the RPM (Revolutions per minute). These DC motors are calm effective and can be utilized in several hobbyist and industrial application.
Reducing the RPM while maintaining high torque would require adding up more technical gear mechanism therefore the price of these High torque DC motors mostly depends on the RPM, torque and quality of the motors.The motor shaft from the base motor though a transmission connects the tiny gear box fixed at its front portion, which Transmission Chain generates the necessary torque while keeping the RPM low, the entire gears and gear heads are doped with thick viscous grease lubricant.
These High torque Motors seriously different RPM’s such as, 5 RPM, 10 RPM, 100 RPM, 300 RPM, 1000 RPM and so on. The cost of these geared motors is founded on the RPM, usually lesser RPM costs a lot more than those of higher RPM.
Applications
High torque and low rpm DC motors are perfect for robotic and hobby applications, thought how big is the motor is a matter of concern since it is quiet large in size due to additional equipment box but still it would save the trouble and cost of adding external gears to the assembly of robots where just the standard DC motors wouldn’t prosper. The High Torque, 
Low RPM DC motors comes with inbuilt gearbox system providing required torque for your robotic software. Hence these motors will be the most favorable choice for the hobbyist robotic tasks and tutorials posted here.