Animate Objects and Fabricate
You have the gold fly out under your command.
Since you have fabricate, use it to shape all the gold into a solid gold figure of a grandfather clock, or a big McDonald's logo, or anything which catches your imagination and doesn't have legs. It is possible that coins don't count as "raw" materials for fabricate, but that isn't critical here; what's needed is that the coins become a single object. It's been established above that this much gold is approximately 8.29 cubic feet, which is about 235,000 cubic centimetres. A human body is approximately 62,000 cubic centimetres, so this item is a bit less than the volume of four humans. That probably makes it a Large object, but the DM might rule that makes it Huge; no problem.
(There doesn't seem to be 5e guidance as to boundaries on size categories; a Large creature controls (without necessarily occupying) four squares on a 5'×5' map, vs a human's 1; a Huge creature controls 9 squares (PHB, pg 191). The DM might legitimately say "hey! this thing is only the size of 3.75 humans but it weighs five tons!" at which point you should attempt to distract them somehow and point out that size categories aren't really about weight; a really heavy pixie is hardly Gargantuan.)
Now, cast animate objects, a fifth-level spell which the party should have access to. You can animate ten objects, and a Huge object counts as eight of them. The spell doesn't define what a single "object" is, so there's a DM call involved with what you need to do to make the coins into one "object" for the purposes of the spell, if fabricate is disallowed. An object doesn't need to be one single material (I think every DM would allow a bed or a broom to be animated, and they are multiple materials together as an "object"), so melting all the coins together into one long stick, or gluing them all to a piece of wood, may be sufficient. Since the solid gold grandfather clock (or glued wood combination, etc) "lacks legs or other appendages it can use for locomotion", the spell description says "it instead has a flying speed of 30 feet and can hover". This means that, as long as your fabricated tunnel is wide enough to fit the gold body through, it can move 30ft. every six seconds under its own power, commanded by the wizard's bonus actions. That's more than enough movement to get it out of the place; three hundred feet of flying speed before the spell duration of one minute runs out. If you can make multiple castings of animate objects then you can probably walk it right out of the city before the guard arrive. Since you have two spare animated objects, give yourself a flying sedan chair and a drinks cabinet too.