2 billion at the high end isn’t actually unreasonable when compared to falcon 9’s costs which are sitting around 100m/launch right now largely due to inflation.

There’s a have a fairly linear relationship between rocket payload and size, and for large structures going big tends to increase cost per pound so ~10x the size resulting in ~20x the cost is just mildly pessimistic.

If and only if they the thing is both rapidly reusable and individual starships are actually used for hundreds of launches do those highly optimistic numbers become vaguely possible. Even just a 0.2% failure rate would represent a massive increase over their optimistic estimates.