I had the same problem when I tried to store my collection of copper jello molds. They were beautiful, but when not hanging on the wall... they were really tough to store. My solution was to eventually donate them... however I won't tell you to do that!
Sometimes a bundt pan, even though it can't fit into another...can be turned upside down and the two will kind of fit together with the two inner cylinders touching (hope that makes sense). Also, can they be stored like books on a shelf, rather than stacking on top of themselves? I know you can keep them this way be using small tension rods, like the kind you'd use for a kitchen door's curtain, only the rods will be placed up and down, rather than side to side....and you'd have many of them, in various width ranges.
Have you thought of going on pinterest and putting "organizing kitchen pans" in the search bar? That may also help.