I believe it is actually more difficult than it would appear, mainly because you need to give people access to the machine to enter the candidates and when you do that, you are potentially giving them access to do other things.
That said, the problem is not insurmountable. I would suggest open-sourcing the software and the hardware design. There are enough people that are interested in this problem that I expect that it would be well supported and potential security flaws found and fixed quickly. It would also greatly reduce the development costs.
We would still need companies and governments to work together to build and certify the machines, but everyone could be working off a common, open blueprint.