Note, this is a (net) carbon free lifestyle within a society that isn't (net) carbon free.

I'm not sure it helps to describe these as costs. Might be a better ad for their app if they framed it as accelerating the transition to saving money/civilization by directing consumer spending towards those working in the right direction.

I'm also not sure how options 2 & 3 (A second option is to purchase additional solar capacity in a remote solar park.) differ from just buying green energy. Guaranteed additionality?

You are MADE of carbon, your breath out carbon, there is no such thing as "living carbon free". This propagandist non-sense.