The navy has had it's own fairly effective anti-air missiles in the RIM series for a while, but there's been a huge push to standardize around VLS and this lets them achieve that and cover a big defensive gap at the same time. As far as I am aware no RIM missile is VLS compatible (meaning they require their own dedicated launchers with space for same), whereas VLS PAC-3 MSE/CRI (1 and 4 missiles per cell, respectively) can just be dropped in - all you need to do is plug it into your Aegis bus and you're set.

I don't know how effective CRI is against the various hypersonic missiles, but if it indeed is effective then it's roughly 1:1 at about USD ~$3 million per Iskander missile - so economically it's viable for the US (no healthcare go brr) to keep up there.

Production-wise, it's... not really possible to know. If next year LM hits it's production target of 2000 PAC-3 MSE without compromising PAC-3 CRI production then... maybe...? Unfortunately neither China nor Russia are as transparent with their military production capacity as the US is, and both countries have a proven history of sometimes just making up those same numbers so losers like me can't have fun.

If we go with the official statistics, Russia has a capacity of 1200 9M723 (Iskander) a year, and china has a capacity of 17,000 DF-17, 3000 YJ-21, 800 DF-ZF... (and the costs for the chinese missiles are just guesswork. We don't even know if the DF-ZF or DF-17 are entirely real due to lack of info, let alone their unit cost) so... Yeah. Maybe?

(I'm guessing here, this is not financial advice, etc:) It's probably technically maintainable, but it would be stupid. More likely will be the investment into low-cost interceptors, lasers, CIWS and expansion of high-simultanious-target combat management systems to go with them with an emphasis on identification, so militaries can be less flamboyant with the high cost missiles.