It depends how high the direct insertion goes. 100km is not a hard and fast boundary for space. Some satellites on elliptical orbits get as low as 70-80km. It's unlikely the LV won't get as high as that but if it doesn't then glide KKVs can be used. I'm also not seeing too many direct insertion HGVs about. The UR-100N is certainly not designed for direct insertion launches.Brilliant Pebbles will not work on a direct insertion HGV, they are also significantly more expensive than a nuclear-tipped interceptor and more strategically destabilizing as well.
The cost with reusable launchers to put the KKVs in orbit will be significantly lower than with old non-reusable one and small fry when you consider the $6tr spent on Iraq and Afghanistan, which is actually more than it would cost with non-reusable launchers several times over.
Nuclear-tipped interceptors are also destabilising, especially long range ones, which could be mistaken for an attack by a 3rd party. They would also reduce the number of offensive warheads allowed under START. Would long-range ones even work unless they were glide interceptors too? Surely a defence against third rate powers (NK, Iran) is actually stabilising too and may even deter some from developing nukes.