My son was 5 and obsessed with “big trucks”.  The only thing he wanted to be for Halloween was a Peterbilt.  So, I used 3 boxes, painted them.  I used tin foil for the chrome, LED push lights for the headlights, dryer vent stacker the exhaust stacks.

He loved his Peterbilt Truck Halloween costume!  It was a huge hit with his cousin and all his friends too. Very inexpensive!