You can't use the old fashioned catholic church approach here.
It is up to the person putting forward the hypothesis to prove that it is so.
So far, there are numerous challenges to the figure quoted...let alone the notion that rampant over reproduction by humans leads to great wealth. One only has to visit countries around the world with high birth rates to knock this pin down.
No. It is up to you now, to prove the figure by laying out the methodology for the calculations in a scientific way.
....and at the end of the day, it is a morally bankrupt view of the world to think that anyone would be convinced that the best reason not to abort would be economics.
Abortion is a subject where those on either side of the argument will not reach any middle ground, unlike the Church's attempts at finding clinical justification for tubal ligation or 'natural' ways of birth control. If you are someone who believes that humanity begins at conception, there will be no way of even reconciling first trimester abortions.
If you are someone who believes that a foetus is not human until the point of unassisted viability outside the womb...then you will never see the side of those who really believe that every sperm (including those spilt by Onan) is sacred.
There is no winning this argument.