You don't need a zipper foot to sew zippers, it can be done with a presser foot or a welt foot. I do this for a living every day, and have never owned a zipper foot. If you want to see how it's done, I will post pictures. The reason there are two "posts" (presser bar and vibrating presser bar) as you call them for the two parts of the foot is that you have a machine with alternating presser feet, commonly referred to as a walking foot.
No one lives forever, the trick is creating something that will.