Maybe a wiper motor with a PicoBoo controller to go up one direction and then reserve polarity to go down. I saw this diagram the other day on Fright Props, http://www.frightprops.com/faq/content/4/133/en/control-a-12vdc-motor-from-a-picoboo.html. This would probably work with your existing motor if reversing the polarity makes it work in the other direction.
I just bought some latex from theengineerguy.com in Atlanta. The have mask latex and molding latex at what I thought was reasonable. My local Walmart had latex in pint bottles for $10 which for the amount seems high.
I use something like it on a grave digger and it's pretty smooth. With a PWM speed controller it works great as you can slow down the movement. The motor has enough torque to move the prop without any trouble.