Most Economic Linear Actuation?

[VegaObscura]

In my opinion, one of the most important parts of a robot is the ability to reach out and do something.  Sure, that could be done with a robotic arm, but I think that would seriously over complicate an otherwise fairly simple task.  I want to learn how to cheaply make a pole that extends straight out.  All the linear actuators I see online cost around $100 and are capable of much more powerful feats than most people need.  I want to find a way to create an extending pole (I wouldn't call it an arm) with a stroke of about 1 foot and material cost of about $15.  Does anyone have any idea how to get started?  Am I being too optimistic with my goals?

[rbtying]

I'd guess a gear rack + gearmotor would do the trick, with feedback from an encoder?

[knossos]

Gear rack + motor was what I was going to suggest too.  Here's a servo-mount gear and a gear rack from servo city.

[waltr]

A lead-screw is another good way to do a linear actuator. This does have excellent holding without applying power to the motor and can be slow/hi-torque or fast/low-torque depending on the lead pitch.

[Soeren]

Yes, plus one for screwing 
For simple apps. a length of cheap threaded rod can be used with regular nuts, however, the thread is not shaped for load bearing, so for powering up, the screw from a scissor car jack is a much better choice - Just look around and you'll find usable screws in different sizes.

An alternative could be a folded arm swinging open by a servo or similar.