Without derailing TOO much, ARs are cheaper than ever to buy, cheap to maintain, excellent at what they do, and are a mature weapon system. Many departments get them for FREE through the DRMO or whatever they're calling it now, leftovers from our previous federal spending.
I've used both platforms, and the ergonomics, reliability, accuracy, flexibility and value of the mini14/30 platform is not even on the same playing field as an AR15. But that's a different topic.