I use one or two of these puppies:
Pad that with some egg foam and a bit more flat foam on top to stop models moving around, and I haven't had a transportation break in months. The most important thing transporting models is to make sure they can't move around at all, if they can roll or slide into each other then they willbreak from the collisions. Squash them between the foam, and as long as spears are flat rather than pointing up into the foam, then they won't break or move around.
I have also seen some very cool metal (magnetic) cases that are worth considering if you are willing to put in the effort. You put (rare earth) magnets on the base of your models and stick them to the case so they can't slide around. You can also magnetise your movement trays so you don't even need to rank them up when you get to where you are going.
A similar in principle but rather novel idea, and not very practical for an army more a single model, is to use a small wooden box. Put a screw into it from the outside, and have a nut secured to the bottom of the base. Then screw the model in to the wall of the box and shut it. That is how people at my local GW were sending models to Golden Daemon, to test the box they stuck a model in it then were kicking it around the store and nothing broke.
And yeah the GW ones are designed for the job, so they can be good, but they're very expensive. Not a lot of people have that much money to burn on just a case.