I know they said they only wanted feedback on numerical balancing, but I'm unsure how difficult or easy this would be to implement so I'll suggest it anyway. I'm also not sure if anyone else in this long thread has suggested something similar, but here's my two cents.
I think the current build costs are probably fine, especially for groups of players and especially now that they have increased CMM supplies to match the demand. However, many of the tier 3 constructions still feel out of reach for solo commanders. Not because it isn't possible, but because the task is so monumental that most won't even deign to try. I'd like to offer an alternative to the grind that doesn't leave solo players out in the cold or give them the same weight as a group cooperating.
My suggestion is that if a colony is capable of producing commodities needed for a new construction project in the system, it should use a portion of its regeneration rate to slowly fill that need. Larger colonies with larger supply and regen rates would therefore supply materials faster. Smaller colonies would not only fill these requirements slowly but may be incapable of filling every need automatically. If this contribution is split between multiple construction projects, it would therefore go slower.
Commanders and squadrons would still benefit from moving materials manually, as the job would get done much faster, but for the solo player that doesn't like the grind they would have the option of simply being patient and waiting for some or all of the resources to fill, depending on the size and diversity of their colony. I imagine the wait time being roughly on a scale of months, weeks, or days for tier 3, tier 2, and tier 1 respectively, but I leave that balancing to the devs and community feedback. I'm also unsure how easy it would be to build a colony capable of producing the most demanded supplies, but that would need to be considered when adjusting the contribution amounts. Hard to tell since we are just getting started.
Edit: I might add that if it's too difficult to implement something like a small, passive contribution, then perhaps the tier 3 stations should cost 153,111 materials instead of 209,122. That would keep the growth in difficulty between tiers consistent, as currently, it increases by roughly 3 times the amount between tier 1 and 2, but 4 times the amount between tier 2 and 3.