Golden Dome currently is an expansion of hit-to-kill technology which means more NGI sites, AEGIS/PAC-3/THAAD/GPI on both shores.
If they can get solid motor and sensor production under control, IMO $50bn (plus overhead and unexpected costs) for missile shield against >1k warheads is feasible. SBI has a kinetic (pLEO architecture using Starshield-like sats) and space directed energy. As I said in an earlier , parts of this plan are very provocative and will drastically increase the proliferation of long-range non-ballistic missiles and ultimately the end of the Outer Space Treaty.
It will be interesting to see if NGI has better performance in tests compared to GBI. Outside of the US military itself, many American analysts seem to think GBI is not a credible system and thus does not contribute at all to deterrence or the thinking of adversaries due to its poor test record.