Cheapest and easiest is the mechanical Trius one-step. About a hundred bucks and lasts for years.
Of the electric ones, I think I like the Promatic best. They're made in the UK but available here.
The Do-All Outdoors trap is cheap, made in China and overall sort of crappy. I have used one for years and keep needing to rebuild it. I think the company may no longer sell them so it might be moot.
It is worth getting a wireless remote - you can easily make one if the machine has a remote foot pedal or push-button.
A wobble attachment is very cool but adds significant height to the trap which may make it difficult to get into a van.
