Many times I will make plywood crates if boxes are not available. Crates can be made for about $350.00 worth of materials and a couple of days of time.
For domestic moves, it can be done cheaper still.
Although I have a pair of bespoke flight cases for my DSP7000s, they were, of course, at the wrong place when I last needed to transport the speakers, as I had nowhere to store them in London.
As all I needed to do was get them into my own vehicle and transport them, the solution did not need to be courier-proof. It did, however, need to permit easy customs inspection as I entered Europe. This was resolved by not having a solid lid but by using ratchet straps to hold the top layer of foam in place.
I made cradles using cannibalised pallets that I was able to scrounge for nothing. These were inlaid with a fair amount of thick foam rubber sheet that I obtained from Pentonville Rubber. This sheet can be built up in layers to ensure stability within the enclosure. I had to use a specialised glue (I think it was one designed for automotive trim, but the rubber supplier should be able to advise). This solution is, of course, not weather-proof but adequate for single movement transport in controlled conditions.
Total cost was about £45.00 and three/four hours of assembly time. I wrapped the speakers in that scratch-proof thin white foam sheet that computers and HiFi units often come in to protect the piano finish from the rougher foam.