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.

[1] https://www.scmp.com/news/asia/east-asia/article/3180997/nor...