IF Colorado did this all alone they could potentially avoid a lot of the high costs that result from getting federal dollars. Maybe - Federally funded projects tend to cost 4-7x would they would elsewhere in the world - but nobody really knows why and so it is questionable if Colorado could figure out how to build cheap. Still the potential is there. Colorado's costs would be a lot higher at 7x the cost with federal funding vs doing it all themselves for reasonable costs - but only if they solve all the issues the drive costs up.

Note that I have no confidence Colorado will tackle the issues driving costs up. Several of the known factors are places where politically powerful people (from all sides so don't bring in class warfare) are increasing costs and they let you cut them off. There are a lot of unkonwen issues left after factoring the above, and it is likely they also have politically powerful people increasing costs.