The economics you're looking at for biogas and electrolysis look roughly right to me. But our models suggest that thermal gasification of biomass can get down to $1/kg. So then you're looking at $4.50+/kg for electrolysis or $1/kg for gasification... and you can see how all that math changes.

Electrolysis also typically costs more than you'd expect as soon as you add the requirement of renewable energy supply. Usually the renewable energy supply is solar, which has a ~30% duty cycle. So 70% of the time your electrolyzer is sitting idle. This crushes your economics and makes solar-powered electrolysis untenable in all of the analyses I've seen. We didn't have any clever ideas for how to change that situation, so after looking at it ~1.5 years ago we decided to look elsewhere.