It's really cheap, fairly easy to make, and well worth the effort if you do any amount of wire work.
I MADE IT AT TECH-SHOP http://www.techshop.ws
Base -- 1 X 8 pine board; about a foot long
Frame and sliders -- 1 x 1 pine; about 6 feet of it total.
Pulleys -- 1" x 1/8"
Fasteners -- Finish nails, Screws to fit the inside of the pulleys.
Step 1: Start the Base
Step 2: Cut the Sliders and Match the Push Rails
Stack them against the base rail and measure for the length of the push rails. Add about 1/16" so the sliders are not packed in too tight.
Step 3: Drill for Push-screws and Capture Sliders
I just drilled the holes in the wood for the machine screws. I matched the hole to the nominal diameter of the screw (not the threads). You could oversize the holes and use nuts and washers if you want.
Step 4: Add Pulleys and Calibrate
Hand straighten about a foot of wire off a spool. Line the pulleys up with the push-screws so that the straight wire witll fit through between them. Then add a little tension to each so the wire is held tight. Use a pair of plyers to pull your wire through another 6 inches and then release. It will either be over bent, under bent, or just right. Keep adjusting and pulling until you pull a perfecdtly straight wire out!