Oh, IRIS-T SLX? That's even more expensive per missile, as it boasts way more components and is larger. Probably over a million dollars per missile, if you think that's capable of providing the cover the Iron Dome has you're delusional. I don't have an exact cost figure as it seems to not exist yet, and no information besides range and guidance is out there.
Israel intercepted 661 rockets in 2021, for an IRIS-T, it would cost 661-1322 million dollars to intercept, way more than the cost of battery, as much as 20 batteries, in fact the cost of battery is irrelevant. For the Iron Dome it costs 27 million dollars, it's 1/25th of that.
Besides, the Iron Dome also has 100% success in trials
Defense Ministry, Rafael complete round of tests for upgraded version of air defense system, which they say has shot down over 2,400 projectiles to date
www.timesofisrael.com
But reality isn't trials.
Mantis gun is useless, it can barely cover a radius of 5km.
Anyways, the Iron Dome battery costs 50 million dollars for export, much less for domestic use.
150km range come from trials, the system has been upgraded, and now has longer range. Wikipedia isn't updated.