I recently built a project with a NEMA 23 stepper motor that direct-drove a worm gear gearbox and the torque coming out of the output shaft is massive! Cheap worm gear boxes are a available, new, at SurplusCenter.com, which is where I got mine. About $120 or so, I think I remember. Still a little pricey, but the these gear boxes are able to handle multi-horsepower motors and the output torque is massive if the gear reduction is high enough. Output speed is slow, sure, but it's a trade-off.