[DonRotolo]

As you noted, these are expensive, in my mind their biggest drawback.

These are better suited for manipulator motion than for drivetrains, particularly because there are far better solutions for drivetrains where space is not such an issue. Think robot elbow instead, where they can be great.

That being said, a cheap source of worm gears for experimentation is window lifter motors. No, they are not strong enough for drivetrain or big manipulators, but you get some nice gear sets for cheap that you can play with and learn.