They don't? Like there's cosmonaut mode which I've done, that goes all in on the idea of not importing anything from other blocs except for the starting stuff.
Money is only used for a few things
- Buying resources from the two blocs
- Buying labor from the two blocs
- Buying vehicles from the two blocs
- Inviting workers from the two blocs
- Transport costs when you don't want to pick up whatever you bought at the border
If you have your construction office set up properly then buildings cost literally nothing