Go to Lowes or your local home improvement center. Get the 1/4" "cheap" ply, 1" X 2" pine strips and wood screws that they sell, and fabricate shipping crates. They will even cut the ply to your demensions for 10 to 25 cents per cut.

Cover your models with plastic, then use a little foam rubber (very expensive) and many spray cans of foam insulation (cheap) to isolate your airplane parts.

I built two crates that held 2 each .40 size and 2 each .60 size airplanes for about $40 total in wood and about $35 in foam.