That's a false comparison. You want to compare between the actual options you have, which are either (a) firing an interceptor (or several); or (b) repairing the damage caused by a non-intercepted missile.
It’s far more complicated than that. The choice is often between firing an interceptor against this missile aimed at this target, or firing that interceptor against the next missile aimed at a target you can’t yet know. Because unless your production capacity far outstrips theirs, you’re going to run out first.
Your first option comes with the major caveat that each interceptor you fire comes from a limited stockpile whose replacement rate[0] today isn't sufficient for even going 1:1, let alone accepting that multiple interceptors are required.
I'd say the real options in the near term when faced with an inbound missile is a) deciding to deplete your stockpile of interceptors with an incredibly limited replenishment rate; or b) risking a hit to a lower-value target.
Could the US go to a war economy footing and scale production? _Maybe_? I'm not entirely convinced the US can stomach the costs.
[0]: again, numbers are hard to find, but https://www.lockheedmartin.com/en-us/news/features/2026/Lock... gives a flavor of just what defenders are up against.