This is hilariously cherry-picked. THAAD is extremely expensive if that's the case. Wikipedia says you can get a Patriot for just $4M. Also SLBM's as actually deployed aren't using maximum MIRV counts, both for treaty and role reasons. Wikipedia says 4 RV's on average for Trident, FWIW. But the big whopper is that you're forgetting to account for the $4B SUBMARINE (just $200M per missile though) required to deploy those missiles in their cost!
Good job though. Honestly the numbers are closer than I'd have expected. But ICBMs remain more expensive.
I chose Trident because I wanted a fair(er) comparison of costs due to purchasing power. If you want to use North Korean ICBM pricing, it's $30M[1]. THAAD is very expensive, that you're right about...but it's also the only interceptor that has a chance of success against an ICBM. Please note as well, trident is typically deployed with far fewer warheads likely among other reasons because it doesn't need to be an interceptor sponge, per its role. If you're North Korea with a small arsenal, every one needs to count against an opponent with THAAD.
Good job though. Honestly the numbers are closer than I'd have expected. But ICBMs remain more expensive.