Yes, there are certainly a lot of variables in the calculation of the overhead costs for bioreactors.
I wish I had more than just 'hope' that the yield will suffice to cover these expenses and then some, but so far I have not seen anything on which to base such a hope. For all I know, they are not even close to breakeven.
So, here's hoping that the Welch's experiment will lead to another bigger experiment, which will lead to revenues, profits, and a better world. Until then, I'm like the kids in the back seat, chanting "Are we there yet?"