Utility scale renewables are in pennies pwr kWh in Levelized Cost, and continually dropping.
There are 10kWh/liter of jet fuel. Utility scale solar is 3c/kWh LCOE today.
Assuming a pessimistic 10% efficiency in electricity to synthetic jet fuel conversion via H2 hydrolysis and the Fischer Tropsch process, that's a hypothetical $3/liter of synthetic jet fuel.
Current petroleum based jet fuel is $1.50/liter.
If you improve the conversion efficiency to 20% and lower the LCOE of utility scale solar to 1c/kWh (projected by 2050), and the hypothetical liter of synthetic jet fuel drops to 50c/liter, all while petroleum jet-fuel grows increasingly scarce and more expensive.
The efficiency of synfuel production could rise significantly as the efficiency of feedstocks like H2 hydrolysis (already 50%+) increase, and if if CO for Fischer Tropsch can be sourced from biomass instead of sourcing it from atmospheric CO2.
Finally, it's likely that in the future we'll switch to using hydrogen directly as an aviation fuel, bypassing hydrocarbons altogether, at which point the electricity to air conversion efficiency nears 80%.
At those prices, you can begin to afford to overbuild renewable capacity to drive a synfuel pipeline to store that energy chemically, which we will arguably need to do for seasonal energy storage anyways.