Best motor for sliding part of robot?

Right now, I’m building a robot that is supposed to go up and down stairs. It will have wheels on bottom of the sliding parts. The modified servo that came with the VEX Robotic Kit is very slow. I don’t have enough money for faster motors. The small geared motors like the ones sold by Pololu cost $16.00 or more but I’m not sure if they are powerful enough. I have two motor controllers sold by Pololu.

So can you explain more how the slide operates, what sort of forces and speeds are involved?

Think of the robot as a CNC router. I'm worried about the weight of the robot which is made from steel pieces. The modified servo is too slow. I use 8-32 threaded rod. I found these geared motors for $10.00 at http://www.campsolution.com/dc24v100rpmgearmotor2-1.aspx

I doubt that motor really is 0.8 watt

So what is the weight?, what is the servo that's too slow? - where are the specs needed to work out
what kind of motor is needed... How fast? What torque?

I tried a DC motor usually used in toys and it moved the sliding part fast enough. The size of the motor's can is 1-1/4 inches long and 1-1/8 inches in diameter. I built one of the four assemblies shown in the photo and I didn't build the chassis yet so I don't know how much the robot will weigh.

Without an idea of the weight you can only guess about the motors.... At least decide a plausible upper limit or you
have no starting place for sizing up things.

I'm thinking of using drill motors with gearboxes for the sliding part of the robot. Harbor Freight has a 4.5V drill for $10 but I don't know what kind of DC motor the drill has. It may be a piece of junk.

You can get the below 6v cordless screwdriver at walmart for ~$9.

I'm going to buy the 6V cordless screwdriver at K-Mart for $9.99.

I think that the 6v cordless screwdriver is too slow for the sliding part of the robot. I tried a 18V cordless drill that I already have and it was fast enough but the drill is too big and too heavy.

I don’t know how to take the 6V cordless screwdriver apart because there are no screws holding the orange body together. If I take the metal “U” shaped pin out, I see a two-stage planetary gearbox. I tried to search the Internet but I can’t find anything about the Black & Decker AS6NG 6V cordless screwdriver. I found out that there is Black & Decker AD600 screwdriver with more torque. Both screwdrivers spin at 130 RPM. My Ryobi P200 cordless drill runs up to 1300 RPM and has 400 in.-lb. of torque. Any suggestions?

A servo Might do the job for short distance otherwise consider a stepper motor.

I ordered four motors at 12 Vdc 2500 Rpm Automotive Seat Motor for $9.50 each. The motors accept 1/8" square shafts that Vex Robotics Kit has.