Plastruct is usually outrageously expensive. But for that "corrugated" effect, you could use some of the corrugated cardboard (with one covering layer only) sold by various crafts stores (I think I've seen it at Hobbycraft). Usually between 1 and 2 pounds for a 50x70cm sheet.
Combine that with the H- or U-Beams (great idea, that!) and it should work out nicely. Additionally, you can easily add damage to make it representative of a desolate urban warzone such as Beirut, Grozny, Beverley Road in Kingston-upon-Hull...