Martin Harris' Battle of Hoth diorama is huge, and includes everything we've seen in The Empire Strikes Back: Snowspeeders, a complete rebel base, a giant snowy battlefield and a some other tiny things.
Computers and displays hanging on the walls, chaos that is somehow organised, rusty post-industrial techno-junk lying everywhere. Tim Schwalf's massive LEGO cyber slums fan-build has it all, just like a proper dystopian town.
Here's proof that you don't necessarily need thousands of pounds to build something unique with LEGO. Although you might need a lot of blue blocks (and around 1,900 pieces total), the simplicity is perfect in BrucilSprout's microbuild of Wind Waker's sea chart.
Even things like the cave on Outset Island (that tiny hole at the bottom of the first pic) are visible.