If you order direct from Evergreen you're paying thru the nose , and then add to that shipping .

I bought four 12X24 inch , 2mm sheets , sent to my house , for about what Evergreen charges for a single sheet not including shipping .

Personally , I use plywood and solid sawn lumber for bases .

But being in construction , I have tons of material .

ABS sheets can be solvent welded too , so that will be an option . It's more rigid on average compared to the equivalent thickness in polystyrene .