Really tough stuff to find used, or at any discount. I think MM actaully sells a torque arm, panhard bar combo at a better price. Give them a call. They had free shipping in September, not sure if they still do.
One word of advice, get the HD torque arm now. I know its more, but the other is a little dissapointing.
I have both, and love them. Big difference. Pics in the link in my sig.
Even if you find them used, they still usually go for a lot of cash. The only place I can think of that might get you a discount is Dave Turner Motorsports in Kearny Mesa California. Great group of guys there.