I've looked into it, but never did one.

The bed needs to be braced with it's own frame, most likely the kit will lift the bed up some since you will have some heavy tubing and bumpers separating the bed from the frame. Then you have the expensive parts, the cylinder should be pretty big and powered by a high pressure pump. The pump is probably the price difference, and depending if you have to have braided SS lines the kit should cost a pretty penny.