In the RRG under Fail, the following rule is included:

“An effect that fails does not trigger any effects that would occur after a ship resolves that effect.”

What about costs where the wording is “[Y]ou may spend 1 <charge> to perform a <boost> action...” (Afterburners) or [Y]ou may spend one <Force> to perform...” (Supernatural Reflexes)? If that action fails, is the charge still spent?

Yes. It's not an effect that occurs after the action it's a cost to perform it.

For the time being, my sense of the community consensus is that costs are spent whether or not the action fails.

I feel like this is the kind of thing where FFG could easily rule the either way if it ever makes it to an official answer. In a lot of cases costs cannot be spent without achieving the effect, but failed red actions still give stress.

yes, the cost is still spent, because a failed effect is still "resolved in a default way".

so you can pay the cost for the effect, because it can be resolved.