A free plane? Heck, not free, but you can build your own by buying foam and designing your own. That would cut costs tremendously. You could get a piece of EPS and trace out something, cut it out then do what you have to do.
We have a guy in our club that made aircraft out of those meat foam packing plates that the grocer or butcher puts meat on. Anything is possible., but you will still need an ESC, Receiver, and servos. Nothing is really free, ya know?
CGr