I really don't get this whole 'districts are too expensive in late game' vibe. If you have overlapping factories and power plants, a brand new city built in the information era, with a trade route going to your capital, and getting factory/power plant bonuses, can build districts in 10-15 turns. Same as normal.
Costs go up, but so does your industry. You just have to make sure at least one industrial zone is reaching the new city. Even if none are, 1-2 trade routes to your high production cities makes building anything trivial. Water mill in 10 turns, districts in 15.
And yes, spaceport costs a lot. Even in my highest production cities with Ruhr Valley etc, it still takes 22-28 turns. With all the appropriate great people cutting space project costs, and the social policy that reduces them by 15% if you have military academy/whatever the last harbour upgrade is, you can build space projects in 12-15 turns. Without them, they take 20-30ish