JohnHill,
Yes worm is good, and this is actually a neck, so it is necessary that it moves slowly.
GoForSmoke,
Well I'm not really sure I could use a pencil there. Also, if to use a servo to be a brake for a dc motor with the aim of making the dc motor function as a servo, then it seems to be better to forget that and use 1 servo from the beginning. I'm still looking if I can put my cnc machine to use for Arduino robot and create mechanical advantage so hopefully: use those 8$ dc motors, some cnc machined mechanics (may be a solenoid) and get a servo-mechanism for neck, which costs in whole less than a 15$ hs-422. This may be a closer formulation of my initial goal.