I can see it working when all parties are trustworthy and committed to fairness, which is a high threshold to begin with. Also, everyone has to buy into the idea of other people being autonomous agents, with no shoulds attached. Still, this might run into trouble when one party badly wants something flatly unacceptable to the other and so unable to afford it and feeling resentful.

One (unrelated) interesting quote:

my womb is worth about the cost of one graduate-level course at Columbia, assuming I’m interested in bearing your kid to begin with.