Torque of locked gear motor vs gearless motor

The cheapest and most common thing you will find is a stepper motor. You can salvage a few of those from old printers and scanners. And if you use microstep control, you can make it very slow and accurate (below the fundamental step of the motor). The problem with steppter motors is that they consume lots of current regardless of speed.

In any case, there are gears that can take a lot of torque. The gearbox in your car does a good job, for instance.

look at modern PMDC washing machine drum motors they often have the all the working out at the rim, and could probably be modified to have a large bore, in a normal machine shop fairly easily. I don't know if spin cycle exceeds 900 RPM or not,

something like this: http://www.fp.fisherpaykel.com/direct-drive-motors/common/pdf/4876_NZ_Motors_BRO_HR.pdf