The empty vacuum of space shouldn't offer any resistance to a travelling electron, and so a large collection of electrons should similarly travel through a vacuum without resistance.
As a result, the bottom line is that an empty vacuum should be an excellent conductor of electricity, since it offers no resistance.
And in fact, this is exactly what a Free-electron laser does:
Here is a Wikipedia article on the subject.
Now, I understand this is expensive gear, but presumably someone could come up with a cheaper version that could offer charges pumped through a difference in potential.
There's another post here, the answers to which, frankly, don't seem to be very useful and claim that empty space isn't a good conductor - that's just not correct, since a free electron laser is a real thing that exists, and does exactly what they said it couldn't, which is pump high voltage.
I found a similar SE post here.
Does anyone know if there's a cheap consumer version that pumps charge through a vacuum?