I would probably 1.5x costs of Industrial, double costs of Modern and 2.5 Future
That does sound likely overcorrecting. Perhaps halve those factors? Personally, I would also prefer a maybe ~10% slowdown in tech across the board. But this also has to do with difficulty level: at higher levels AI gets a boost, and since tech costs depend on how many has researched it already, so do you in keeping up. In my current game (immortal, epic, normal size map with 6 civs), Washington just entered renaissance in 120AD, and I'm about one "column" behind in the tech tree.