Upon my latest trip to a Dollar tree store I took a shortcut down the toy isle.
I saw some "Lego clone" bricks and glancing down I saw some storage boxes for them. They are 2 toned and the top has the "round pegs" for the use of them as a base to build on, where the interior is divided up into sections.
Hmmmm.....$1.25 for a great, cheap project box or chassis, WOW!
i couldn't find anything for this price anywhere.
I'd suggest grabbing them while you can still find them, as the chain is notorious for having limited quantities of items and a short stocking duration.
2 types. blue box with red top, and red box with blue top.
They seem to be reasonably sturdy also. Cut out the dividers and turn the box upside down for a chassis. Use your imagination!