[Magesmiley]

You might consider using some of the plastic shoeboxes you can get from Costoco in a multipack. Glue some foam (such as pluck foam) inside and you have a pretty inexpensive solid container with foam inside to protect everything.

Also, FWIW, I'm liable to use 3D wall pieces for my games. Specifically stuff made using the Hirst Arts Castle Molds and number of bags of dental plaster (you can get it in grey even). There's also a very good chance my next (3rd!) battlefield will be built using them.

There are a number of molds that are suitable - particularly in their sci-fi and factory stuff, though it probably wouldn't hurt to rally the folks here to request some more post-apocalyptic specific molds suitable for Car Wars scenery. My one request probably won't get too much traction, but 3 or 4 requests might.

On the battlefield, I suspect that it doesn't matter too much what the size is as much as it matters that the boundaries are clearly delineated.

You might want to think about storage if you're going to do some 3D stuff too. 3D walls and jersey barriers will most definitely look cooler than cards and counters and are a relatively simple upgrade to do.