Some scrap foam, glue, and $2 for 2 bottles of flat craft acrylic and a Batcave might be born 
foam
Rocks from the garden, foam, a hacksaw blade, and cheap paint is hard to mess up, even with "no measuring allowed" and "speed painting" with a 1" house painting brush it looks like "something"..Heck the grey brick was mostly snapped to length vs cut.
There are a few alien / sci-fi threads that may prove interesting too; the Phantom makes appearances. If you must own all things Batman there is an M7 subway engine & Joker/ Harley cars; Justice League, and at least two Batman cars to go. I'm surprised I haven't seen an official Bat signal spotlight car. That seems as no brainered obvious as the Marvin the Martian Earth Disintegrator Rocket Launching car was.
A clear Phantom shell or cut into a "gondola/flat car thingy" and a Batmobile load? A mech like an old tin auto unloader (Marx or American Flyer?...automaticaly twists the flat bed near 90°, the bed tilts, and the car rolls off it. Very cool, especially when you consider it's age.
I wanted one to pull a Looney Tunes space train but I never really found one. At least not a reasonably priced one, so I made something. Which works too, but the Phantom is just cool.
Does it have a Bat symbol in the car windows as illustrated pictures have shown? A Dark Knight shot?... I mean dim light shot? And if it isn't trouble, a straight on overhead of the engine, maybe angled 45° for front from above. I just wanted an image to manipulate and the image hunter didn't find my rose.. 
