I thought that a peristaltic pump is a better option for paste extruders than some that I have seen. Update: Added hotends, and added a hole for the mounting plate so it will fit correctly on stepper motors.
Note I have NOT made this, I believe it will work but don't know for sure.
I'm designer for shapeways here: https://www.shapeways.com/designer/jonathanmarch/hire-me
Print: Mounting (you can design your own easily), Base, Rotor and Top
Also print a hotend of your choice .5, .75, 1, 1.5, or 2mm
You will need support for the base but should be fine with everything else
Assembly should be self explanatory just refer to the image.
8xM3 screws are needed
4xM3 nuts are needed
Whatever length of 2mm ID, 4mm OD, bowden tube
3x608ZZ bearing (the most common bearing I believe)
22mm OD 8mm ID 7mm height
--You may have to glue the bowden tubing in so it doesn't move.