Internal Growth or Immigratiion

For this question I'm assuming that for the first few Island One's and perhaps even into the Island Two series, that transport of a colonist is expensive so that there is a natural incentive towards high birth rate in the Habitat to try to lower the demand for immigrants. I think a prerequisite for building these things is cheap flights.

I've been studying this, and flights as cheap as about $2000 per person in todays money is theoretically possible; that's the asymptotic price of the fuel anyway. It seems reasonable that the cost will eventually reach this price, if nothing better comes along.