Sub-Frames on Non-Vert worth it?

It was the first thing that I did on mine. Had a Fox body previously so I wanted to nip this issue in the bud early on. Fox4 chassis is strong but still needs some help in the stiffness department. When I had mine installed on the Cobra, could feel an increase in stiffness, especially when I drove the car over an uneven surface for the first time with them on. So I would say go for it.
 
Try this.

Take out your spare & jack. Take out the trunk carpet/floor. Take out the entire backseat. Turn your radio off and drive around. make sure to make some turns and go over some uneven road. You'll be able to HEAR the car creaking and twisting. It's amazing. I don't have them, but I want to get them.

Where is the best place to buy them, and how much should I pay?
 
Man I need them too. I think Ford shoulda just put the damn things in at the factory along with 3.55 gears in the first place! Somebody else said it best in another thread about not having sub-frames when they talked about hitting a few minor bumps in the road and "rockin' and rollin" all over the place.