Almost definitely billions and almost definitely multiple years. Planning, testing and clean-up alone could be over a year. It's far too early to even put a number on it.
Even if we assume $600m is the correct number, the expenditure is evenly distributed, and it takes 6 years to be fully up and running. Based on 3% inflation alone:
Year 1: $100m, Year 2: $103m, Year 3: $109m, Year 4: $112m, Year 5: $116m, Year 6: $119m = $666m
Even if we assume $600m is the correct number, the expenditure is evenly distributed, and it takes 6 years to be fully up and running. Based on 3% inflation alone:
Year 1: $100m, Year 2: $103m, Year 3: $109m, Year 4: $112m, Year 5: $116m, Year 6: $119m = $666m