Thinking about it I could probably make one out of pallet wood, some of that wood is pretty good stuff (and cheap) once it's cleaned up. The latching mechanism looks pretty easy to make, just a bit of welding required. The hardest part would be drawing out the pieces so it will actually work, then it's just lots of time!!
I hope you're making scaled drawings of yours as you go, ClaimedVacancy (hint,hint).. It's looking good so far.