well, you had me until this post.
your volume is so low you can absolutely afford to pay candidates. given that your setup process is also automatic, it's offensive that you aren't.
a candidate 'invests' their entire day's output in it and gets paid $0.
your team 'invests' their entire day in the project and gets paid $XYZ dollars.
are these equal "investments"? obviously not.
you can afford it - paying candidates will be a business write off for you anyways.
you're just not doing it because... reasons?
really lost me with this post, it doesn't sound compassionate at all. you're using candidates the same way everyone else is, but the bar is so low that describing the process and giving feeedback got me excited.