Assume $1k/kg for LEO insertion. That means a metric ton of iron, in space, would cost a million dollars if you had to ship it from Earth.
Let's now say that you wanted to build a large space-based manufacturing facility, focused on producing high-value goods like zero-gravity metals and pharmaceuticals. Shipping the raw materials from Earth to build the facility would cost around a half-billion dollars, and then afterwards, you'd need to ship them the additional materials from which to produce the goods.
Or, you can do something crazily ambitious -- figure out how to get the materials from somewhere in near-earth-orbit, and use that to bootstrap both interplanetary travel and space-based industry.
It's crazy. I know. It's crazy enough that it just might work.
Personally, I'm excited. This kind of ambition is what we need as a species right now, and I'd rather see the money spent on this than on yet another collection of mega-yachts.