How can I move a one-ton gem out of Undermountain?

Looking for some ideas on a particular conundrum my party is faced with. We’re in the depths of a dungeon in Undermountain and have come across a literally one-ton gem. We’re all 9th level and are a bit stumped as to how to take this gem out from the Undermountain, intact, to the outside world where we can profit from it.

Here’s a little more detail from a fellow party member:

  • The gem is a perfectly crafted dwarven ruby that is roughly a sphere with a diameter of 2.5 ft to 3 ft.
  • The ruby is located on a short (~50ft long) platform on the 8th basement floor of the Undermountain. The only access to this platform is a rope/wood bridge that is in incredibly poor condition, such that my half-orc ranger, weighing 250 lbs with all equipment on him, barely crosses the bridge without it collapsing.
  • The bridge is about 60ft long, and when a torch/sunrod is dropped down the chasm it covers, we lose sight of the light before it makes contact with anything.
  • Through adventuring mishaps, we have access to 8 total party members, 4 of which are magic users. Two party members (the half-orc ranger and an NPC warforged… something?) each have an unmodified STR of 20
  • Getting assistance from outside of the Undermountain would be… difficult. We rappelled down a chasm to get to the door of this floor, and then teleportation was involved further on this floor, such that we don’t have a path back to our original ropes. We have a lead on another stairwell that might lead up to the surface, but there is no guarantee that we have a direct path back to the surface.