Saw some talks years ago by Daniel Nocera, in which they did water splitting and fed hydrogen to engineered bacteria to make more complex products. Cool stuff - I'd imagine the end products, fuels in their case, would still be way too expensive.
There's interesting stuff going on in modifying microbes to make cannabinoids and other natural products. Would be kinda cool to combine these two :)
I agree, Daniel Nocera's team have done some really cool research and you're right that renewable fuels in general would be too expensive. I would argue that the cost of fossil fuels are artificially low because their current cost doesn't account for the environmental damage they cause. If we had to pay their true cost, the difference might not be so great.
I like to dream and so our long term ambition is to try and make complex molcules like cannabinoids directly from CO2, but we're some ways off.
We need to campaign to make these costs clear and keep companies accountable